You can have Home Depot do your cuts, just have them cut everything 1/2" long or so. Then, just trim everything up to true specs. i just have them cut the sheet in half, as i don't have a truck. I have to put the MDF on top of the car usually.
Home Depot has a sign by the saw that says "No project cuts", but slip the guy a tip, and you would be amazed how well they can do project cuts.
To summarize:
1 sheet 3/4" MDF: ~$25
1 5/8" screws (I use drywall, they seem to work well) - $5
Bottle of Titebond III - $5-10
Tape measure
Table saw
Jig saw or Router
Good drill bit and countersink
~$50 for a MDF box.....plus carpet and adhesive if you are going that route.
Good luck. I enjoyed building my first.