Budget isn't that low. Entrance fee $300, Drysuit is mandatory for open boats - $450-$800, PLB -$550 (you can rent one) Lights, knife, charts, GPS, camping equipment, specific for the Challenge,etc - another $500-700. It good to have more than one GPS. Fitting oars and testing them prior to Challenge, it can be done relatively cheap, but amount of jokes from fellow catsailors should weight in.

Boat preparation - you will need to recut and fit reefs to mainsail. Get a furler, if you run a sloop.
All new rigging, all new hardware.
Drybags. It's better have best ones. I normally pack smaller bags into big ones.

Staying at the finish. There is great party starting with second finisher and lasting until last one gets in. Three-four days. Normally there a place to crash right after the finish, but for next few nights you will need to find your own place.
Logistic to get back to your trailer and car.
The price tag is getting big, then you put all this little things together.

Expirience is priceless <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

Here is a video from the start. The Windrider team didn't make it further than 1-st checkpoint, but video gives a good idea of the different types of boats racing
http://www.windriderforum.com/stuff/EC2007.wmv