I would probably buy it for $30. Make sure it has a bobbin case, as those can run about $25 to replace. Also check to make sure the wiring isn't crumbling or brittle, as that costs extra to fix. If possible, try it out and make sure it forms a stitch. (You can do that even if you can't plug it in, just by manually turning the wheel.) The ability to form a stitch is sort of a key test for me. I pass up machines that do not form a stitch because they may need retiming, which is something I don't know how to do. Cost for a technician to retime is often around $75 or so, and can run more.
You should be able to clean and oil it yourself. You can often find sets of extras for a machine like this on eBay, but for additional $$$. You can also often find parts online, such as here:
http://www.sewingpartsonline.com/whi...ine-parts.aspx