Personally I think its a crap idea to have a permanent charity slush fund.
Administering any kind of fund is a nightmare. You will end up with a disproportionate number of dissatisfied folk.
We all get caught out now and then and have to resort to raiding the building society , flexing the plastic or grovelling to the bank manager. Been there, done that.
However I'm sorry to be blunt but if you cant afford to run and fix the motor you buy you shouldn't have it.
A good mate in the trade told me years back look at the most expensive uninsured bit on your car that might conk out. If you cant afford to fix it or just walk away (even if doing either causes pain) don't run that type car. Personal circumstances may change that for some so each case should each be dealt with on its own merits.
Look at what this club is, its primarily a friendly advice and social set up, its not Disasters Emergency Committee.