Im using and fixing them since 19, (my first bike was a non running Kawaski ELX100 - which I rebuilt myself using the repair manual, a simple tookit and an old dining table).. and Ive repaired quite a bunch of expensive 2 stroke machines - I was known as the insane person who loves deadly 2 strokes, (H) I used to gun my rebuilt RGV250 alongside big bikes. These single RX engines are stupidly easy to rebuild, For cylinder builds, most of the time it is cheaper to just buy a used cylinder, as firstly proper porting takes a good part of 1 or 2 days, not to mention a good pressure cast cylinder sleeve is very expensive to buy (quite more than what the lathe shop charges you for a whole sleeve job) - then getting some dry ice or nitrogen for the sleeve to shrink and carefully reaming out the old sleeve from the barrel and heating it in an oven while measuring the very cold sleeve and very hot barrel. Then carefully pressing it in the hot barrel - once cooled it will hold the sleeve super tight like original. Its expensive but worth it for a machine whose cylinders are hard to find. (the above mentioned RGV250 is an example)
I'll give you an example, sleeving an RX cylinder this way may cost you about Rs 7000/- to Rs 9000/- (cheaper to buy a used jap cylinder)
The sleeve job you will get from the dumbas$ shops have port aims all wrong and very sharp edges like glass, and the sleeve becomes loose if you just heat up the cylinder with a torch this causes siezure and the wrong port aim and sharp edges cause bad compression and broken rings