Get a Mill's Pride C13 Cabinet from Home Depot and stick a 400W or 250W light in there. It costs $99. Drill 4 2" holes in the bottom for ventilation and one 4" hole in the top for exhaust. Also, drill one 3" hole in the bottom to run your wires. Take 2 black 2" 90-degree pvc plumbing connectors for each hole, and make a light trap. Attach these underneath the cabinet to the holes.

Stick a cheet of 3/8" or 1/2" plywood on the back for support, and hang your light and fan.

You can also get a C22 for more room.

Mill's Pride may have discontinued making the C13 and C22, but you should be able to find something. Some great places to look for cabinets which you can convert are:
-Home Depot
-Lowe's
-Wal-Mart
-Target
-Ikea (really! I've seen several cabinets from Ikea that have been converted).
-Crate and Barrel, possibly
-Any discount furniture store, really

Good luck!