Most clubs are pretty strict on the helmets, tends to be an insurance compliance item if something were to happen. You should be able to find some older, cheaper helmets. Keep an eye out for sales. I think I got my 2010 open face helmet for like $140 2 years ago from Dave at Solotime.
As far as auto-x'ing a bone stock fox-body, you are in for a treat. They don't turn, they don't brake, they like to snap spin, they like one-wheel peel. They are bonkers. If you are mechanically inclined, I would check the posi. Also, grab a cheap set of stock spare wheels and some craptacular street tires. You will learn more in a season on bad tires in a fox-body than some people learn in a lifetime of driving Miatas.
You're going to want to crank up your front PSI to 40ish to prevent the tire from rolling over (fox bodies lose a ton of camber in turns). Probably set the rears around 32. A stock fox-body is fastest when it is kind of floating around, skating around the course; i.e., you'll kind of pitch it in there and wait for the car to catch up. You'll get the hang of it after a few runs. Be sure to ride with some experts in other rear wheel drive cars so you can see the course, walk the course with them, ask them to ride with you, etc. Keep a full tank of gas in the rear, these cars are nose heavy and you have stock suspension. Don't run a staggered wheel setup. No goofing off in the paddock, pits, or roads near the event site.
Drive the piss out of it and you'll have fun.