If you have a computer, the cheapest I think you could go would be
Chamsys MagicQ Magic
DMX basic. It cost $16 plus shipping and handling. It's a full 512
channel universe of computerized
DMX control. The program has a steep learning curve though. The other catch is that you can only use it for 5 hours before you have to restart the program. If you don't want to deal with this constraint, then the full version
dongle is available for $100.
If you want to go stand-alone, search eBay for a
dmx lighting controller. If brand is no concern, one can be had for about $100. If you don't need physical control of each
channel at the same time, then one could be had for less.
Good luck!