If you are a cheap bastard and barely use your phone, there are plenty of plans out there for $30 or under that have limited minute and data setups.
If you need to use your phone more than a few hours per month, then stepping up to some unlimited plans is where you need to be.
Here are the options depending upon your area. Prices vary based on number of lines and data cap needed.
1) Straight Talk - $45 a month, 2.5 GB data until being throttled, and unlimited otherwise. Great for a single line and uses the AT&T network as well as the Sprint Network if you have a CDMA phone.
2) Metro PCS - About the same as Straight Talk just $5 more.
Neither of the above carriers have contracts or help you out with phones. Phones available are limited, but either company allows you to bring any phone compatible with their network. You will just have to buy the appropriate sim card and then do a little programming to get your phone on the network. Customer service with both carriers is crap though.
3) Cricket is similar to the previous two, but has more phones and phone financing available. Still not as many phones available for it as the big 3 carriers though. Customer service is marginally better.
Now if you are doing multiple lines and need unlimited.. T Mobile tends to be king here for price for plans. They finance phones separately with no interest. This is what I switched to recently with my wife. She was on Straight Talk for 2 years while I've been with Sprint for almost 17 years. Most of that time on a SERO plan with Sprint.
We went with T Mobile 4 lines for $100 bucks. Unlimited talk, text, and data. Although 4G LTE data is capped at 2.5GB per line. We don't go over that. Most of the data usage we have is with streaming music which doesn't count towards data usage on T Mobile from the major streaming applications. We both got new phones, the LG G3, with the 24 month payment plan from T Mobile. Phones are $25 a month on top of the service plan. Once paid off, you don't have to pay that anymore. T Mobile offers a 15% military discount so I'm only paying $85 a month for 4 lines right now. I have 2 extra lines, and I might just let either friends or family use them for a small $20 a month charge.
The other thing with T Mobile, if you get 4 or more lines, they throw in an extra mobile data line for a data device like a 4G ready tablet. Of course you have to own the tablet, and the data is capped at 1GB for 4G's speeds per month. Still it's an extra bonus you don't have to pay for.
So the outcome is this. Previously wife was paying $50 after taxes and such on Straight Talk a month. I was paying $60 with Sprint after taxes. That's $110. My service with Sprint has always sucked. Spotty connections and shitty data speeds. Hers has always been great connections. Straight Talk and T Mobile use the same network, so for me it is a massive improvement in usability of my phone. We are paying $85 + $20 (insurance on the phones which I only like keeping for 1 year) + $50 (for the phones and taxes are paid up front) + $10 in fees/taxes on the service plans. Bringing my total to $165 for now per month. Once the phones are paid off and I'm done with the insurance my costs will be $95 ish per month. Cheaper than what I am paying now. I get better service, new phones, and better connectivity for myself. If I make some money off my other lines I can shave $40 off my bill doing that.