Like other cars in the RX series, the RX-4 used a Wankel rotary engine. This car got the larger 12A engine at first, and the even bigger 13B engine after 1974.
These cars were sold as a 2 door coupe, 4 door sedan, and 4 door station wagon.
These cars were only sold in the United States from 1974 until 1978. All of the RX-4's exported to the U.S. had the 13B engine, which produced 110 horsepower. It had improved fuel economy over the RX-3, which was considered a gas guzzler even by 1970's standards.
The original retail in the United States was $4295, with air conditioning and automatic transmission costing extra. It's safe to assume that RX-4's with those options are rarer than those without them.
These cars are not easy to find on the used car market. You've got a better chance of finding one on eBay, where you can search sellers from across the nation. You might also be able to find some rare parts on there.