Try eBay or Amazon. Or put flyers in wood working stores and woodworking guilds.

Expect $1 per board foot as is. If you can prove it's not hollow or straight-grained beyond the first 4"-5" or prove it has an eye pattern then you can get more. This burl is not overwhelming the tree so it's not going to fetch a high price. If you find a local woodturner, to supervise the cutting, that would be your best way to go.

There are some good forums on wood cutting and sawmilling. Just search "sawmilling forum". WoodWeb and Norwood come to mind. You can probably get some good detailed info and advice there.

I don't think there's any way to prove what a burl looks like inside. A friend of mine has cut a number of burls - one was enormous - and it turned out to be pretty boring inside.

AnnKH, of course there is a way to prove what a burl looks like inside. Cut it open. An eye pattern is detected by slicing the outer edge (the "pole"). And the inside is determined by slicing it along its latitude, as well as, by cutting it into plugs.