Post the link here. Open the site, right click on the address bar at the top of the page, click on 'copy'. Come back to the QB, open your entry, choose 'edit' and the choose 'edit' from the toolbar on your computer. Click on 'paste.' Then we can look at it easily.
In general, any vintage machine that isn't rusted beyond recognition is worth $20.
I just looked and didn't find the machine you're referencing, but I did find two 401s - one for $40 and one for $50. The $50 one would be coming home with me if I were closer! Or the other one for that matter.
http://stcloud.craigslist.org/art/2431963827.html
Found it. How fast can you get there? That doesn't look like a 501 - the 501 has more of a Jetsons look, but it something from the 400 or 500 series. The 501 may be Singer's best electric machine, but any are worth buying. I lile my 301, but sew on a 401 at quilt guild and it's a nice machine.
I just looked again. It may be a 501. I repeat, how fast can you get there?