I paid way too much for my whiteboard ($25-ish), which I'm still bitter about, I didn't even think to shop around for some reason (too much beer?). When I cut my frame from the plastic on the door I left a little lip on the inside for the whiteboard to sit under, I cut it to that size. Good luck!
Nlanzillo, check out my blog, I had the same issue, this might help you make some decisions.
http://www.fattonytcl.blogspot.com/2012/12/how-my-little-kegger.html
I used painters tape and a circle saw. I think any saw would work though just make sure you keep your board from vibrating too much. The excess parts without the painters tape chipped a bit so thats a step I wouldn't recommend skipping.
This pic shows the white board after it was cut.
The only extra advice I can give is to be as gentle and patient as possible, I was only half joking about the machete...the blade would long enough to cut from the edge of the door to the different raised parts of the insulated areas. If you can cut the raised parts off somehow from the front...
I just completed my Kegerator build. I've posted a fairly detailed walk-through on my personal blog. This thread helped me a ton, thanks guys!
Walkthrough
Two Pin-Lock Kegs hanging out together!