EG,
Everyone knows that SEO is hot, and getting hotter. The importance of ranking well in Search engines, can save big $ in the long run vs PPC advertising. There are also plenty of sales comparables with they keyword SEO. The good ones range in the x,xxx neighborhood. However, the fact that this is a .us does hurt the value quite a bit. I would probably value this domain at < $150...
Good luck!
Justin