As far as I know, the Gorilla Pad can be bought for ~$150 for a 24' round pool. Happy Bottom is more expensive and you have to cut it and tape it yourself. The Gorilla pad comes cut and seamed to size.

The main reason I'm looking at the Gorilla pad is to provide a barrier to ants. The guy who repaired the ant holes for us last fall said that any kind of foam bottom would be just as tasty as the vinyl, so it wouldn't ultimately provide any real protection from the ants.