If it's an opamp-based amplifier, you can't really deviate too much from the datasheets and still expect anything useable to come out, so pretty much any opamp-based amplifier is related to a CMoy. And really, a CMoy is just an amplifier based on the opamp data sheets with slight modifications.
As to whether or not the RA-1 is overpriced, it's probably not fair to compare it to a DIY CMoy. You can't just look at the cost of parts and say that it's too expensive. There are other things that go into the building of an amplifier, particularly one that is sold by a small company through audio dealers. All of the normal corporate overhead has to be covered, the manufacturer has to make a profit, the distributor has to make a profit and the retailer has to make a profit. So, sure, the amplifier may only have $25 or $30 worth of parts, but that's only part of the cost of manufacture. After all, even your time is worth something!