10X10 is a weird size if that is what you really are looking for, they are usually 5X8 or 8X10. The good ones are not cheap, I like Integral Designs and you can get the 8X10 sometimes for $80 on ebay. I hear good things about Tarptent also, you might want to give them a look. If you want dollar value get the blue tarps at walmart for $3 but they are bulky and weigh more.
BB