You missed the good part of the T-Mobile PAYGO plan: once you have paid the $100 once (or accumulated it via smaller payments), all your future added minutes last a year. So if you haven't used $100, you can top off with $50, or even $10, at the end of the first year, and it roll the leftover minutes forward to the next year and add the new minutes. If you buy fewer minutes, you are paying a bit higher price per minute, but you never lose the old minutes as long as you top off. This is why the original purchase of $100 is worth it, since you get the best rate ($0.10/minute).
Also, T-Mobile has great deals on refurb phones often. I bought a Dart (not a great phone, but it works), For $90, which came with a $50 card for minutes. Thus, a useable Android phone for $40. It does support WiFi data tethering, so I can pay the $2 or $3 rate for a day when I need data, and have that for my other devices, too.