2003 CR 125 question?

It depends, if you do the work yourself and the cylinder isn't gouged and messed up, you can do it for a very reasonable price. If you take it to a shop and tell them to fix it whatever it takes and costs, they will more than likely take you for a ride, goodness knows how bad. A Wiseco top end kit (piston kit and top end gasket kit) runs around $130 or so on eBay, Wiseco top end bearings run around $15, the flex cylinder honing tools you use in drills are relatively inexpensive (around $30-$40, though it depends on which you buy and where. If your cylinder doesn't need a $200 replating or anything like that, you could do it for well under $150, add $30-40 if you don't have a honing tool, and that's talking a complete top-end rebuild with top-of-the-line parts.