You can look at the competition on CL using adhuntr. Only one 2007 in the SF area shows up. The owner started out at $1100 (wacky!) and brought it down to $850 after 3 weeks of no-sale. There are a few that show up with different years with asking prices between $500 and $800. See: all | Ad Hunt'r - Search ALL of Craigslist? and more!

It is a 55 cm (21.6") frame. That refers to the distance between the center of the crank and the top of the seat tube. It is the way frames are measured on traditional frame bikes. If you list the frame size in the ad, seasoned riders will know if it fits them and not waste your time.

Don't forget to set the seat height so your leg is just a tad bent when the crank is at the same angle (parallel to) as the seat tube. That gives you the most efficient pedaling