your best bet would probably be to ask the man himself, heh.
But off hand, I'd say most cab designs I've seen need 3-4 sheets of MDF @ around $20 each. Then you'll need some miscellaneous 1x1, 1x2, or whatever would work best for some support beams in the cab. Maybe $10-15 for that stuff on the high side. A few bux for some boxes of screws, you'll probably want some glue too.
I'd say $120 would be a good guesstimate for just materials. That's assuming you have all the tools needed though, and is just for the basic structure. You'll probably need hinges/locks/bolts/whatever else you plan to put on the cab. Hope that helps a bit.