If you buy your groceries at Kroger store (Kroger, FredMeyer, Smiths, Ralphs, CityMarket, Bakers, Fry's, WFC, Dillons, KingSoopers, Gorbes, etc...), you can get 20 mins free on their prepaid phones for every $100 you spend at their stores. Then its 20 cents per minute on their $0/month plan or 10 cents per minute on the $5/month plan. Pretty nice if you shop for a family. If you are creative, you can add several shopping cards onto your account and farm free minutes from your friends & family whenever they shop.
https://www.iwirelesshome.com/whyus/freeminutes/
The phones are $20-60 in most stores, and you can buy them online also. They usually bundle free minutes which make the cost of the phones effectively free. One interesting feature is that you get unlimited incoming text messages for free. The phones all use CDMA/Sprint network.
Any prepaid phone will force you to periodically buy minutes in order to keep the account open. I think the minimum on the Kroger phones in the form of prepaid cards is approx. $10 for 60days or $20 for 90days. Your existing credits and minutes will rollover, but regardless of how much you actually use, you need to purchase that amount within that time period to keep the number and account open. This can be done on credit card using their website if you prefer.
Also - if you just need a phone strictly for emergencies. You don't have to pay a dime. Any old cell phone you have should still be able to dial 911, even if its no longer activated etc...
Good luck!