I had my old motor completely stripped down, all the componants measured (including all the gearbox) the rebuilt with a new rod, 102mm JE piston, valves & springs, gas flowed head, clutch springs and all new gaskets and seals throughout. At the end the engine was meticulously vapour blasted and repainted (it looks like a new engine now, not the old knacker I took in). Total cost was around £1,000 including all the parts and labour.
Compare that to doing the same tune on an in line four or something else, like a KTM/Honda/Yamaha/Husaberg