I have found an ad for a 2005 Burley Sandpoint for only $550. I think I'm going to go and have a look at it. Any opinions?

Burley specialized in beginner-to-midrange models. The Sandpoint was one of Burley's 'checkmark' frames - monotube shaped like a checkmark. Definitely not made for speed (95 inch top gear sort of admits to that,) but would make a decent commuter. They retailed for $750USD; I'd probably try to talk them down a little bit more for a 3-year-old bike.