Stag-dos have to be inclusive. That means lowest common denominator.
People being pushed beyond their limits just breeds bitterness and resentment, as does subsidisation. Whether that be genuinely honest hard-up folk with understandably wounded pride, or whether it be better off generous folk feeling rinsed by classic car collecting freeloaders.
It sounds like this situation is toxic. People will drop out or limit their committment, which pushes prices up for the others, which encourages drop outs, it’s a vicious circle.
I’d be cancelling the house (not in a huffy way), apologise for having overcooked it, and just have a night out in the pub.
Cameraderie, bonhomie and general good spirit by far the most important elements of the occasion to preserve.