Hey, guys! Look at this! Zelda: Parallel Worlds was a real game cartridge!! LAWL
...Yeah, I don't think what they're doing is right. The amount of money asked for doesn't sound like just wiring, soldering and what-not. I think it would have been a safer and nicer thing if they just post up how to do your own reproductions, if you're into that.
Also, they say that what they're doing is legal... Not quite, I think. Doing this for yourself is perfectly fine. Doing this for your friend is questionable, but it's fine. Making a business out of this, is not.
That site has always made me ill. As an electrical engineer, I know it costs less than that for the materials. However, they also say you're paying for the 'time it takes me to build the cartridge'. That's where the bulk of the price is going. So, in other words, mostly profit. I think I'd have more respect for the guy if he didn't have all that advertising of "products" and offered a quiet service of making custom carts with whatever the client provides.