Like most car racing, rally has a fixed "base" cost to get out on stage.
This figure is $10k if you pay someone else to do all of the work. This will get you out on stage in a car with suspension that won't be blown at the end of the rally, and all the various safety equipment/vehicle equipment (skid plates, cage, seats, etc).
That is NOT including the price of the car.
Now, Metros aren't very durable cars. There isn't really a reason to run them versus other vehicles as they aren't (IMO) any cheaper to buy or maintain then a lot of other econoboxes. And because the base price of a rally car is fairly well defined, you have to try and make it have some value if you ever want resale, which means having some power and being able to be used in G2.
Spec a car you can get in perfectly fine condition for $2k or less (no rust, not miled out, around 100hp or more, durable chassis/suspension) and build your spec class off of that.
Surprisingly enough, this is NOT a MK2/3 Golf in my opinion. The standard motor options are incredibly lackluster, with the 16v gti motor being adequate. I'd argue that realistically, the Neon is where it is at. And everyone and there mother has a cheap neon with a blown headgasket somewhere! This was tried in Alberta, but there was no buy-in. A pity, because if someone did nice prep work on built to order spec rally neons (the only spec thing would be stock motors and trannies with a lsd allowed, and weight, nothing else would matter then besides driver skill even if everything else on the car was baller bling parts y0)