not 100% sure if all manufactures use same type of foam. But I think most are polyolefin foam. The problem is the well reviewed pads and ones that hold up to some abuse are made of layers.
If you want the cheap route buy the Sam's Club offering for $250. Many are happy with and some say they ripped a hole in it first season and they ended up buying a more expensive one with more layers anyway.
If you have a few <100lbs kids playing on it you will likely be fine. If you will have more 100 some pound teenagers playing king of the mat it will likely not last as long. If you have a drunk 200lb buddy that jumps off the pontoon or boat onto the mat, you will likely have a hole in it.
Foam isn't as cheap as it seems it should be. Then add into the cost to ship such a large and bulky object and it costs even more.