A mate of mine did the very same thing when he was helping out setting up a site, worked really well and I think thye managed to strike a bit of a deal with the garage for a few quid to take them away, even managed to blag some old tractor tyres from a local farm.go to your local garage with a transit van and take away all their old tyres!
you can make ANYTHING with them...
thats what my field is mostly made out of...
u can even make a good snake out of them lol