They'll charge whatever the market will take / put up with. Although the pricing is indeed weird if you think you can get a used genuine 414 for ~$500, and a brand new one for ~$1k (or less). Not to mention it'll cost you another couple hundred for a good capsule & transformer, and then the time & parts to design (or hire someone to design & make) you the electronics to fit that body.
Then again, it surely doesn't cost Neumann / Telefunken even $1k to put together a U47, and yet they'll charge you ~$10-15k for the privilege of buying one. Iphones allegedly cost $4-500 to make, and yet people will gladly shell out over $1k for one, just because.