Hi mate
I replaced my piston and rings together at around the 90 hr mark. Easy job and I'm not a overly experienced bike mechanic. Just follow the easy step by step guide in the sxf engine manual (which can be found and downloaded from the members section), it was a while ago but I think it took around 3hrs. You'll have no problems doing it yourself, it will save you a load of money and give you a feeling of great satisfaction when you fire it up for the first time.
Cheers