What do you mean, exactly, when you say crankshaft ? Do you mean that one of the crank arms is broken, or do you mean the spindle shaft that the crankset is mounted to ?
Either way, having an LBS fix it would probably cost more than the bike is worth. If it was mine, I'd find a donor bike, either a five dollar yard sale bike, or a junker from the scrap pile, and I'd fix it myself.
Sheldon Brown's website will help you learn how to do it yourself.