I know we've been discussing predominately Sprint, but there ARE other options.
I used to have a T-mobile plan when I first got married that was $49 a month for 2 lines and 600 min altogether. We were cheap at the time, and I like GSM phones (plus their data was the cheapest at the time... $5 unlimited for EDGE). After taxes, my bill was something like $54.xx or so, $59 when I had to start paying for data (for the first 6 months t-mo had free data).
Nowadays, its not really advertised anymore, but someone told me if you ask you can still get it. If you really want the bare-bones cheapest plan, this might be the way to go.