If you're thinking "really cheap" then I guess you're going to put an existing engine in it rather than buy one. In your 1st post you mentioned both 40 & 60 sized planes.... Do you have both engines?

I'm not sure about the Avistar, I've heard that the tail falls off on a hard landing....

A 60 sized equivalent (and a lot stronger) would be the Hobbistar 60 MkIII but its a tad over $100......

The Superstar 60 is getting cheaper every day and was around $97 when I last looked but its a flat bottomed trainer..

The Brightstar might also be worth looking into. They are around $93 right now... (40 size low wing trainer, flat bottom wing)