Card Shark does good work! I've ordered a couple custom cards for a packet trick I created. But you're right, not super cheap unless you order bigger quantities. Now for creating a couple custom cards, it was only $14 bucks including shipping from Germany. That is a steal in my opinion - but not so good for buying a bunch of decks.
Another option that is that you can make your own cards. Chris Wasshuber, over at Lybrary.com has developed a do it yourself system for making flawless custom cards on Bicycle card stock. It's a little bit of an investment to get started - although if you already have a laser print your costs might not be too bad.
I've already ordered card stock from Chris and printed some cards for a game I invented. I used a roller cutter from the local print shop but that style of cutter was not accurate enough for card magic. You need something designed for playing cards. For about $150, Chris sells a die cutter and another $30 for the corner rounder. He also sells the card stock paper and a special coating for cards. And you need a laser printer that is of suitable for printing on the card stock (or go to a local copy shop). So after all of that initial cost, the price of printing a custom deck is about $5. Not too shabby.
Chris meticulously details the process of making your own cards. Check out the pictures of the cards. http://www.lybrary.com/make-your-playin ... -a-11.html