In How to make a custom set of playing cards - Approach 1 I presented the approach I currently use to make playing cards for games I am prototyping. I think it is the best approach, but it is not the cheapest. This instructable shows a previous approach that is cheap, easy and surprisingly playable. The only real downside is that the area for customization is quite small.
For this instructable you will need:
1) Your card designs
2) Cheap pack of playing cards
3) Mailing labels
The playing cards can be picked up at the dollar store (2 packs for $1 at my local Dollar Tree) as can be the mailing labels. That means you can create 112 unique cards (these decks have 4 jokers) for $2 in supplies.