When I started in Pattern I flew a Epsilon 90 with a OS120AX . . awesome combination, and great flying plane. Although I have never flown one with a 90, I am not sure I would want less than the 120 in it.
Jas has a new thingy he is testing at the moment . . Eon 110? . . looks trick (pic of it below). Seems like it may go well on a 90, but Jas is using a 120AX. There's a little bit about it over here . .
http://www.rcuniverse.com/forum/m_9110170/tm.htm
I am not sure the 90 would be much cheaper to run than an OS120AX really . . do 18 flights on a weekend instead of 20 and you would probably be there. Don't think you would miss the two flights
Cheers, JB