hmmm, so I am looking at buying the S4...
where would the best place to buy a google edition S4?
There's only one: Google. Of course, Google is horrible at selling actual items.
Also, it will be the same hardware as the T-Mo (maybe with a different design on the -- removable -- battery cover). So yes, you should be able to just flash the Google firmware onto the T-Mo version.
Anyway... I was thinking of the 50 dollar plan since every place I go has wifi. I doubt I'll be downloading 15Gig movies with a cell phone so I'll have to keep the home wired.
That's the cheapest option I can see with an S4... Any better ways to go if I don't want a 2 year contract?
That's the cheapest postpaid option. Notice that T-Mo doesn't do contracts even on postpaid any more -- you just have to pay the phone off (if you did installment plan) before you drop them.
I would also consider two cheaper prepaid options, if you don't need to roam on AT&T (postpaid gets roaming, prepaid doesn't):
(a) $30 plan -- 100m, unlimited texts, 5gb data
10c/m overage but you need to leave some extra money in the account ahead of time
(b) Straight Talk $45 plan -- unlimited everything (in theory)
The AT&T version of ST has been notorious for throttling, cutting you off after a certain amount of use, etc. But from what I can tell, ST on T-Mo has been pretty much wide open from day one. I dunno if things have gotten harsher since they switched over to only selling T-Mo SIMs, but it's at least worth a try for a month.