What do I photograph? Nature. Landscapes, mostly. Sunsets. Waterfalls. Animals, bugs. Portraits, some of the time (generally available light, and a bit of flash-lighting). Very rarely, action - kids soccer or basketball, tennis, etc. Some birds in flight.
First of all, ignore all replies on this thread that do not take your shooting needs into consideration and instead talk about that poster's shooting needs.
Second, give up on full-frame. Since you talk about costs, you should not go full-frame because the camera and lens makers milk FF especially hard, and it isn't necessary for your purposes anyway since you mostly shoot landscapes, presumably at low ISOs and large depths of field (lower-noise high ISO and small DOF being the main reasons to go full-frame). Furthermore, full-frame lenses are typically bigger and heavier.
I would NOT get Sony A7/r/s unless you really understand what you are getting yourself into in terms of pricing, and are ok with much worse autofocus tracking than you'd get with the A6000 (or E-M1 or GH4 or any midrange-or-higher DSLR). All the FF cameramakers milk the living **** out of their FF users due to lack of competition... FF is a low-volume, high-margin business catering to pros and people willing to pay pro prices. APS-C is highly competitive with so many cameramakers/mounts/lens producers jammed into that space, so you see better pricing than you do with FF. M43 has somewhat less competition than APS-C and lower economies of scale in some cases, so once again you get milked more than you'd expect based on production costs.
And lastly, consider this: the A6000's low-light performance is about the same as the original Canon 5D from several years ago. And the A6000 has dynamic range almost tied with any of the best FF cameras. Sensor tech keeps improving! So what's left of FF's supposed advantages? Not much. I personally think extremely shallow DOF in FF is a gimmick anyway so I could not care less about the somewhat larger DOF in APS-C, but I know reasonable minds can disagree.
Third, you don't shoot much action, so it's not necessary to get top-end DSLRs which have lagless OVFs and good AF tracking ability. Given YOUR needs, mirrorless becomes an option. The Oly E-M1, Panny GH4 (with Panny lenses only), and Sony a6000 autofocus and track moving objects at least as well as comparably-priced DSLRs.
http://www.imaging-resource.com/PRODS/sony-a6000/sony-a6000-shooters-report-part-ii.htm The Nikon 1 series does even better, but since you prioritize landscapes, I would go for a larger sensor than that. If you're ok with good single-shot autofocus but lousier-than-DSLR tracking ability, you can buy an older model like a E-M5, GH3, or NEX-6. I wouldn't do it, though, since you said you sometimes shoot action, just not nearly as much as landscape.
Personally, I'd go mirrorless if I were you. I have similar need as you (mostly landscapes, sometimes portraits and macros, occasionally telephoto/action) and wound up with a Sony a6000. I was so happy with it that I sold my Nikon D5100 and most of my Nikon lenses.
Just a few mirrorless advantages:
Size/weight. Since there is no gap for flapping mirrors, wideangle and normal lenses can be made smaller and lighter than for DSLRs. The advantage goes away for telephoto lenses, but you don't shoot much telephoto anyway.
Video AF. Most DSLRs still stink for video, whereas mirrorless cameras can autofocus a lot better.
Focus Assist (especially with EVFs). All mirrorless cameras give you depth of field preview for free, whereas you have to use live view on DSLRs unless they are fancy enough for DOFP. But since mirrorless cameras with EVF allow you to look at a nice EVF instead of a washed-out LCD with sun glare all over it, mirrorless depth of field preview is easier to use. Ditto with focus magnification. And Sony mirrorless cameras have focus peaking which outline sharp edges in color. This can be used in conjunction with magnification to make it even easier to tell when things are in focus. Great for manually-focused landscape shots.
Live histograms. Like focus assist, a lot easier to see with an EVF in bright light, can alert you to over/under exposure problems very quickly and even in video.
Adapters mean huge bang for the buck. Mirrorless, especially Sony mirrorless, can easily adapt older SLR lenses of any mount, including long-dead mounts where the lenses are cheap but good. You can buy cheap manual focus lenses and affordable adapters and all you lose is autofocus, but for landscapes and most non-action shots, who cares? Note that older mf-only lenses often have smoother and larger focus throws, allowing you to fine-tune focus more easily than with most af lenses. I recommend the Nikon "E" series as an example; they are designed to be small and light and have optical qualities almost as good as the hefty full-blooded Nikkor lenses.
Long-term you won't need to replace lenses if you buy the right ones now. If you do buy SLR lenses, buy Canon because at least they have adapters that let you use SLR lenses on their mirrorless cameras without too much of an issue (STM lenses especially... non-STM lenses may autofocus slower on Canon's mirrorless systems), unlike Nikon (still no DX mirrorless). You should know that almost everyone will go mirrorless at some point in the coming decades. The pro sports market will probably favor lagless optical viewfinders and high-end PDAF for quite a long time. However, everyone who doesn't need that level of responsiveness will probably wind up with a mirrorless camera in the end simply because mirrorless cheaper to make: no PDAF to calibrate, fewer moving parts, no mirror or pentaprism and OVF assembly. EVFs will presumably keep getting cheaper and have higher refresh rates to reduce lag time. And that's not even considering mirrorless's size/weight advantage. Those claiming SLRs have better handling with long lenses should know that you can make mirrorless cameras bigger and heavier if desired, but it's impossible to shrink DSLRs beyond a certain point, due to the need for flapping mirror.
Among the mirrorless options, I would say that Sony has the best overall system right now, all things considered. They have the top market share in the USA and aren't leaving the market ever since imaging/photography/video is a core business. My second choice would be Canon, but only if you don't want an EVF, and I'm pretty sure you do want one. Anyway, Canon will never leave photography/video as a business unless they go bankrupt or something, so while their buildout of their mirrorless line is slow, the lenses are good quality and you probably won't get stranded. Oly/Panny lose money on cameras and might not always be in cameras, given their CEOs posture on money-losing divisions. They are still safe choices and micro four thirds is almost as good as APS-C if you don't mind the squarer aspect ratio. It's just that they are slightly less safe, that's all. After that there's a huge dropoff... Fuji and Leica are basically specialty makers at this point, going for low volume, high margin products and definitely not bang-for-the-buck products. Ricoh/Pentax's mirrorless is a joke due to tiny sensor. Samsung and the rest are even less committed to the photo/video industry, so there's an even bigger chance of getting stranded if they leave the mirrorless market.
Nikon still has no DX mirrorless so they should be shunned by landscape photographers until they do... the 1" Nikon 1 cameras have less dynamic range, iffy controls, iffy long-exposure options, and cost way more than they should unless you buy the old models on clearance.
Mirrorless has disadvantages as well: EVFs have lag and OVFs do not. But you don't shoot much action. Mirrorless also eats up batteries a lot faster, but the easy solution is to carry spare batteries. AF-capable lens selection is also potentially an issue especially in the telephoto range--but you don't shoot much of it anyway. And if you are willing to go MF, you can adapt a TON of old lenses for cheap.