$250 won't cut it. I really like my AXI 2826/10 and highly recomend it on a 4S2P lipo pack. The motor and speed controller is found here:
http://www.hobby-lobby.com/brushless...axi.htm#282610 and I use a pair of iRate 2600 4S packs found here
http://www.unipros.com/cbpsite/fpack...sion_id=132829
You could substitute 12-14 cells of Nimh 1950 or 3300, but it would be heavier and not fly as long.
Looks like around $450 to make a really nice conversion.