Not sure what to tell you on fair price but that's pretty low miles for a 2003! Well even for any year of Silverado SS at this point but especially a first year truck.
If it's from your local area I'd inspect it VERY closely for rust although with 35K miles I seriously doubt it was driven in any bad weather. At any rate the hard lines for brakes and fuel tend to rust out very quickly on this generation of trucks if they're ever exposed to road salt or possibly even salt air (like from the coast) so check 'em as closely as possible.
With those miles I'd say it's unlikely to have signs of problems of any kind. Some believe that low mile older vehicles are full of problems but I'm not one of those. One exception would be the tires; if it has ancient tires (check the date codes) then you'll want to replace them immediately - even if they're not dry rotted.
If it does have any odd details, post back with your findings and others can offer advice. The truck is probably worth well upwards of $15K if it's clean.