Doing it yourself or getting a shop to do it? I did a headgasket replacement on my 96 Zx600, it was $50 for the head gasket and about a week of disassembling and reassembling when I had the time to work on it, shouldn't really take more than 3 or 4 solid hours of work if you have everything ready to go. A v twin might actually be slightly easier if it is push rod controlled, I tore the top end off an HD Evo motor, measured clearances, and put it back together all in 3hrs for class. When you don't have to mess w/ overhead cams and cam chain timing, it's a lot less of a headache.