None of the Sprint android phones will work directly on Boost the way some WinMo phones would.
Your choices are:
Get an approved android device and pony up $55/mo (less in time with shrinkage)
Clone an approved PAYGO phone ESN (Incognito for example) into a Sprint android phone and use that for PAYGO service as you would a WinMo phone
The first choice isn't cheap, the second is (according to some) illegal. If you are going to go the second route I would strongly suggest taking the time to figure out how to do it yourself rather than relying on one of the many "services". You need to have possession of both phones at all times or who knows what might happen.