We haven't had to price them ourselves, but did you check with Big Brand, Costco, Sams Club, Big O, (or other tire stores in your area)? You might even call Jayco direct (574-825-5861) and ask how you can order one from them that might match your current wheels.
We have had two blow-ups over the years
. I'm reallllllly happy we had a spare. Both times we were unfortunately over 30 miles away from help.