An even cheaper option would be to get a noname crap one off ebay. Picked one up for like 35 shipped for my cab. Actually lasted much longer than I expected. Finished the cab and it still works great.
A dremel should have the power to cut the mdf, but you would need some sort of mount or holder to make it work. Also, I don't think you can get slot cutter bits for a dremel. If you could make a mount to control the depth of the cut and attacht the bit somehow, it would work.