I had a cheap one once (about $15). It did not make much of a difference. A better one might have done more, maybe.
I bet a cookie cooling rack would be about as good.
Make sure the fan vents are not clogged. If you are adventurous then you can take the back of your computer off and clean the fan and heat sink (piece of metal connected to the fan). If you are very adventurous then you can remove the heatsink and put some thermal grease on the top of the cpu and put the heat sink back.
This is much harder on a laptop and you can easily screw it up. Get a guide on the Internet before starting.