1. Rare
2. Very fast even compared to todays high performance cars.
3. They are considered Japanese supercars
4. They have lots of potential for power.
5. They are very popular to modify and are sought after.
They are expensive because both cars are usually bought then modified for racing so it is difficult to find one that is still all stock. From what I have been told the Supra is usually used as a drag race car and the RX-7 is either turbocharged, has a 3 rotor 20b engine swapped in, or both.