Yup, it's pretty much the expense that stops anyone from making them.
When I first started making decks, prototypes were about $200, and hard-copy uncut sheets were a built-in part of the proofing process.
They now do digital PDF or JPG proofs as standard - you have to ask if you want hard proofs. At one time the cost of a cut and assembled prototype deck was $1,000. I've not ordered a prototype deck in several years from them, so I'm not sure if they've shifted the cost again.
As Don says, for about $12 you can get a perfectly serviceable prototype from MPC. The stock/finish isn't the same as USPCC, and they tend to print a little on the darker side than what you'd expect from your files, but it's hard to complain at that price.