I've found tractor supply to be a bit expensive on tires. Unless you need new or an extra set of rims why pay extra. I've gotten good prices from internet like stop n go tires. They have free shipping specials on carlisle. I have no affiliation with them other than having bought from them. Summit racing also has good prices on carlisles, but never seen them have any shipping discounts. Hope I'm allowed to recommend sources--didn't check site rules on that.

Is it easy to get them off and back on the rims?

I used an independent tire shop to mount them and there is a local tractor supplier/sales that does it also. Same should be available in your area. I think cost to me was about $12.50 per tire (actually I think I paid $40 for all 4--but was quoted 12.50 per) unmount old, mount new and including new stems and that was for mounting 21-11-8 bar tires.