I find that the mats are waterproof, but the seams are not. So if your rabbit is going pee on them a lot, you may want to put something under the mats to protect your floor.
They are made of foam, so can be chewed. Some rabbits like to go for the edges, so using duct tape along the edges and seems can be helpful. I have also found that putting duct tape on the spots where a rabbit chews or digs helps prevent then from chewing more.
You can find them at most hardware stores as well as other department type stores, stores like Walmart or Target should have them. The cost can vary, but they are generally around $15 for a 4 pack (each mat s 2X2ft). They do go on sale from time to time, usually for between $7 and $10. There can also be sets with 6 mats that a a bit more.