I dont think modified is that expensive. Motors usually last longer (you can throw a wind instead of going up a tooth :P ). But everything else will have a slightly shorter life (tires, drive train, etc). Nothing dramatic, specially at club racing.
If the traction is low, low tech chassis (cyclone S, T2R, XXX-s, ...) might actually have an advantage. All of them have their particular pros and cons. Xray is usually stronger, but belts dont last long in modified and is one of the most expensive. Cyclone S will require some optionals to deal with mod motor properly, but its fast car. XXX-S is a pain to work on, and not particularly strong, but itīs road manners are still very good.
I would choose the best deal - with replacement parts preferably