This Machine Design article is an interesting read for those interested in R/C and turbine aircraft engines:
Engineers have managed to shrink the modern jet engine until it is small enough to fit in model planes. "After a half century of R&D, the turbine jet engine is now more powerful, efficient, and relatively quiet. Development has also pushed the envelope in one other dimension: jet engines are getting smaller - a lot smaller. Hobbyists and model enthusiasts now have reliable turbine engines widely available for radio-control (RC) model jets, turboprops, and helicopters.
Model turbojet engines are generally 3 to 5 in. in diameter, weigh 2 to 5 lb, and produce between 12 and 45 lb of thrust. And adding gearboxes makes the engines suitable for propeller aircraft and helicopter models, providing excellent power-to-weight ratios. Prices for jet engines range from $2,000 to $4,500 and up, depending on size and accessories...
Much more interesting information in the article.