For the most part, anything you pay is usually worth it for a Crosscheck. Surlys are the Toyota of the bike world, you definitely get the most bang for your buck.
That price sounds fine to me, as long as the bike fits. I'm going to do that one more time in bold AND Italics: as long as the bike fits! Ask the seller if he'll let you take it on a full ride (30-60 miles) and bring a multi-tool with you to adjust seat, handlebars and stem. If you find that you're uncomfortable in any way, it's not the right price.
My friends are in the same category of bike people. If you didn't find it in a dumpster, you paid too much, haha. And they're totally justified, really. A good friend just crossed the country on an 80's Fuji he got for free. You can pretty much make anything work.
My LHT is the most I've paid for a bike. I think it's the most I've paid for anything, actually. But if I were ever to buy a new bike again, it'd probably be a Surly, again.