Here's what I use.
Pantech Burst - unlocked gsm smartphone. Has very decent hardware (1.5ghz dual core, 1gb RAM, 16gb memory + microSD card slot, GPS, 4g LTE, etc). The only downside is a weak battery, just recharge every night and you're good.
You get it from Ebay, just search for "pantech burst unlocked". For some reason, prices have gone up since I bought last year, but it's still the best bang for your buck. I recommend getting a "mint condition" one for $95 from one of the two powersellers who provide them, I bought a new one for the Mrs. and a mint one for myself, but couldn't tell them apart. I bought 6 more mint ones for family members, and they're extremely happy.
As for a plan, I use Lyca mobile prepaid. It comes to 2 cents a minute. If you don't talk a lot (ie under 1000 minutes a month), this is a great plan. Minutes don't expire as long as you talk once every three months. For me, I barely scratch 50 minutes a month, so it works out very well.