I went with E-Flite Power 32s, 4s4000 lipos and 60 amp Detrum ESCs for my Twotter....
Total power system cost including batteries was $270. (motors were $70, ESCs were $20 and the lipo was $45, per side.
Hard to beat electric power for the H9 Twin Otter....no cylinder head or muffler cutouts, improved reliability and they give a very nice simulation of scale turbine power!
I got mine together over the Christmas break and maidened it on 12/30/11. A really great flying model!