It's an
R––it will not have mud rails or a rolled slide.
You need to get a feel for the trigger––make sure it is smooth. If there are cosmetic issues, make sure you can live with them. Refinishing is expensive!
There is a
thread here by Max229 about how to guestimate round count.
There is a
thread at SigForum about how to determine age by serial if the original box or date sticker is missing.
If it has nightsights, and they are bright, I would not go for Sig's service package. The thing that makes that worth it is the nightsight replacement. You can buy a P226 parts kit from Top Gun Supply for $25 IIRC, that has all the springs you would want to replace in a high round count gun (or just for peace of mind).
Bruce Gray has the best black guide rods I've seen if it has a plastic or hollow one and you want ot replace it.
Given what I have seen on GB.com and in local shops in CO, I think that is a good OTD price assuming it comes with a couple mags...