I just bought a refurb BSA 4x40 A/O airgun scope from Natchez for a mere $24 + shipping. Looks like it was just a return, it hasn't a scratch and was new in the box.
A couple weeks ago I bought a BSA 3-12x40 A/O airgun scope from Sportsmans Guide for $30 + shipping.
Look around, there are places selling scopes pretty reasonably.
I did have good luck with the Bushnell Sportsman 3-9x32 A/O on an untuned (harsh) B18 for a couple years. It held up to the recoil just fine. I still use the scope, although I sold the gun awhile back.
Jack