A few people have 'ice packed' their cameras to keep them cool. Plastic clip top lunch box with a couple of those plastic freezer packs inside with the camera. If you insulate the lunch box and keep the camera dry it is worth playing with for a cheap 'try before you buy' option.
My cool box starts with a lunch box. I'll post pix when it's looking a bit more completed so you get a better idea of how I've attacked the problem.
A cool box will take a while to chill a camera down due to contained thermal mass and the sensor being hidden away inside but it's a simpler approach for DIY and it does help.
A properly cooled camera uses a cold finger to the back of the sensor to acheive a faster, lower and better controlled temperature but that is really an experts project or a very brave amateur.
