It took me for a first attempt around 1hr 40mins from arriving home (running on one cylinder having limped home from it seizing) to get the tools out, let it cool down a bit, make a tea and chuck another piston and barrel on and fire it up again, in the fading light outside on the road. This includes 10 mins spent swapping the studs over onto of the "new" (read secondhand) piston/barrel set as the HRC head conversion means one stud in the std barrel is too short and two are too long anyway. Then five mins reading on the workshop to check which way the piston clip should sit. I'd guess Andy or Steve can do a cylinder in way under an hour, in fact it took Steve more like 15 minutes to fit a barrel (to a semi stripped bike) and took me longer to change the battery (no really, it did).
The cost depends what you want to do;
If it's just tired or you're paranoid it about time to do it don't replate the cylinders for the sake of it if there is no cylinder damage, they don't wear out and replated cylinders are notorious for the chrome coming off if it siezes in the future. Do the rings by all means, do the pistons if they're worn outside of service limits butthis is not a nice sight to greet you and it's only one you see after a cylinder has been replated, it means your post seizure one hour rebuild just became an engine out, crank out job.
Do it yourself, not only will you save money and learn about your bike, any fear of it eating itself will completely vanish as you'll know how easy it is to fix.
Years of overly complex 4 strokes have taught us anything that lurks under the fairing is too complex to fiddle with, requires specialist tools, skills and years of hard earned knowledge.
Not here
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Please do not PM me technical questions, if you can't find it on the Forum start a thread