Thanks for the information Don and Will.
The USPCC website says a minimum of 2,500 for custom cards, but I'm assuming you have contacted them and received more options. In my experience working with their custom cards division I have learned there are options not mentioned on their website. For example, they may be open to splitting a print run of the cards and tucks into 2 versions with different ink colors to make a Poker Set. The artwork for the decks need to be identical though because they will be using the same printing plates for each run.
There is one major printing difference between MPC and USPCC, Expert, and Legends. MPC does not offer metallic inks or foil on the cards. They offer foil on the tucks (only 3 colors available), but I have not seen a metallic ink option. USPCC, Expert, and Legends offer custom PMS spot colors, metallic inks, foil, and embossing. MPC is 4 color process only.
For prototypes I have used The Game Crafter. They are good for printing early prototypes. A printed deck with a coated textured finish to simulate a good deck of playing cards is only about $10.00 (shrink wrapped). The quality is good enough for photographing the cards. Their custom tuck boxes are not good for photography though because the stock they use is too thin.
A prototype deck with the tuck box printed by MPC is about $25 - $30, the quality is good and will work for photos and videos. Plus as Don says, if you use MPC for the actual printing of the decks it will be an exact match. I am assuming they use the same printing equipment for prototypes and long runs, but I may be wrong.
MPC also has a Rigid Box option, which is a box like the ones used for board games. It's an interesting option and the cost is not much more than a tuck box. The colors on the Rigid Box are not an exact match to the cards though and a few test prototypes might need to be printed to get an exact match. They also have custom Poker Set Boxes and Brick Boxes.