I taught on one of these for 5 summers in the 90s in S.Africa. They are great for fitness and also for beginners to learn basic techniques on. If its just for your own use its possible to build one or get one built for you pretty cheaply. I have been thinking of building one but I dont have space at the minute.
A couple of rollers, electric motor, chain drive, lots of plywood and some industrial carpet, and some steel for the framework.