One should never refer to other people as amatures unless one knows how to spell amateur.
I've been considering offering built chassis for sale, and have been wondering if I can get the price down to £650
(admittedly for a finished chassis, not like chummy is offering), so how he thinks he can do it for that price I don't know.
If it's genuine he must be reckoning to just throw the chassis together. More likely though is that when he gets an order, and finds out just how much work is involved, how much material and other expenses, then he will be re-thinking the whole thing.