The folks at
http://www.infinitehobbies.com are selling the Thunder Tiger F-91s right now for $184.99 with free shipping.
The TT F-91s is a strong, reliable .91 4-stroke that isn't as popular as some competing models because it weighs in about two to three ounces heavier than the O.S. Max .91 Surpass and the Magnum XL .91 RFS. For a plane that tends to be tail heavy, however, the TT F-91s may be the perfect engine.