lowering temps, in summer

summer is around the corner, i don't have central air, i have no room, nor money, for a wall unit and i'm already having temp problems with my cabinet.

so who has some cheap, easy methods of lowering temps?

p.s.- my light is vented, and i have a fan going. i need something really clever, like........ having a big chunk of ice delivered each week and storing it within the cabinet........or maybe someone has plans for a microwave that works in reverse??
could i just steal the good parts from a tiny refrigerator?

i'm going to need a good 10o F drop starting next month.

One thing that will help is moving your ballast out of the grow room if you haven't already.
Install white window shades, drapes, or blinds to reflect heat away from the house.
Close curtains on south and west facing windows during the day.
Turn off lights and appliances around the house when you're not using them.
Consider planting things outside that will create shade for your house.
Direct more air in an out of the entire house, not just your grow room.
Consider replacing all your household bulbs with fluorescents if you haven't already.
Next time you have your house reshingled, use lighter colored shingles.
Consider relocating your grow to a basement or lower level.

Some of these things will help immediately, some of them are to think about for future projects. I hope this helps... best of luck.