Sanded off all that gnarly wood putty, drilled holes for the feet, gave the bottom, insides, and outside walls a coat of black. Then I dredged up a can of stone texture I had laying around to do the sides. Obviously this will need repainted black when it dries.

Dimensions are about 14"x11" at 5/8" MDF for the control panel, the side panels are 13.5" and 10.5" by 4 at 1/2" pine 'hobby board' Bottom boards are roughly 10.5" by 2" wide and maybe 3/4" thick. USB cord is just going to dangle out of the bottom for now.
Approximate consumable costs thus far:
4x8 sheet of MDF - $20 (I've already used most of this for two other countertop machines)
3 sheets of 4x24x0.5 hobby board - $3/ea. I bought an extra in case I screwed one up, I think I could have used it for the bottom.
USB mouse - $6 (I went through several to find one that would work with an Xbox)
Xbox USB adapter - $7
3 cans of black spray paint - $1/each
1 can of stone texture - $8
4 leveling feet - $3
Betson Trackball - $20
Trackball Mounting Plate / 6 pushbuttons - $20
4 pack of L-brackets - $3/each. I used two packs.
T-molding - eh figure $10 worth
Wood Putty - $4
Various wood screws - $5
This hobby is NOT for the financially faint of heart. This trackball is coming out rock solid, though.