You have lots of options, if wanting more power, including a different cylinder, bigbore, porting etc.. etc.. a rebore should run around $50 plus new piston & gaskets.
If you do need a sleeve installed make sure you have someone reliable do it, of course not as much of an issue on air cooled.
FYI
Some 2 strokes cylinders are plated so there are options of sleeve or replate, bore & replate.