The ONLY way to do it properly is to make it a spec class. Chose only 2 or 3 different airframes and 1 enigne.

For eg:

Tracer 40
Venus 46
Tai Ji 40
Ultra Sport 40
(or something similar)

TT .46

Now you have a cost effective class where pilot skill becomes the real difference. But alas these things only tend to work in club level type stuff.

The only place I have seen this work on a large scale was when I used to race boats years upon years ago. The basic starting class was 3.5cc OPC. Small boats only one real engine available and the best racing you've ever seen. A sight to behold seeing 6 of these rounding the last turn together.

Then again if enough people get on the bandwagon it might just work out okay. There are lots of these planes around so it would be easier to get some of the sport fliers involved.

If you limit sizes as everyone knows the money factor will still be there (see F1 car racing for proof). The only way to reduce the money factor is to specify airframes and engines.