The Tormek one is really expensive, they start at about £400. Though the this basic one, the T4 is pretty much identical to others on the market costing far less.
A Record Power version(8″ wheel) will cost you £170, others like Triton-£250, Scheppach Tiger -£140.
The RP one has a host of free bits, dressing stone etc and is probably the best deal overall.