If you don't snatch it up at that price, please please please tell me where to find it! Seriously, just take it to a Singer repair service center (and there are even repair centers for older machines; I've been in a couple). Have it cleaned, oiled and looked over. It might need a belt or something along with that new plate. At any rate, it will be like getting a brand new machine back. You don't want to find out about any new problems when you're deep in the middle of a new quilt!
The owner of a second hand repair shop for Singer is a friend of mine (went to high school with him. His wife was my best friend.) He says Singer is really invested in keeping the old Singers in good repair, and why not? Can you think of any other sewing machine from the 1920's that is not only still working, but working well, and has parts available? It's a big part of their reputation and image as a "Dependable Machine", so they won't let you down. Oh, how I wish I had my Great Grandmother's treadle machine! Wouldn't you know they just junked it. I cringe every time I think of it. Oh, well. Water under the bridge. . .