I've dabbled with Octave Mandolin, Bouzouki and Tenor Guitar, as they can all be tuned the same (EADG, high to low). Great fun to play, and the Octave is [i]much[/i] easier to navigate those thick bass player fingers around than the teeny tiny regular mandolin. Tuning is in 5ths, not 4ths, and the chord shapes are totally unlike guitar, but if you're willing to put the time in it's a very rewarding instrument to play.
There are a few mid-range makes out there, especially if you consider tenors and bouzoukis as well.