There is no reason that you couldn't build a rally-legal and -appropriate first-generation RX7 for something more than the cost of a spec RX7.

There used to be a ton of them out there but they have faded from popularity. Even at that there should be a good knowledge base from which to work. You would need a sound shell (a consumable in the world of rallying), twice the amount of safety equipment, a rally-legal cage (a little different than for road racing), a computer, basic suspension, and rally tires - which are expensive and can get gobbled up even with modest horsepower.

Initial licensing is easier than club racing, probably because a driver can be a loon and be a threat only to him/herself. In essence, you attend a ground school of sorts and then its on-the-job training.

Logistics are a pain in the butt so start calling in markers for help, not the least of which being someone to serve as balast and on-board navigation system. Don't call me: I'm retired after 10 or so years in the right seat.

Kirk