Welcome to the board! I have not owned a 401, but have a 403 and 501, so guessing in the 30lb area. Where I live, around St Louis, they are regularly listed for $100 or more and I believe sell near listing price because the ads aren't up long. I would say $50 is a good price, as long as everything on it moves, meaning can you turn the hand wheel by hand and does the needle go up and down, how easily does it turn, do the pattern dials on the front turn and lock into all the positions, does the needle position lever move the needle, stitch width, etc.
There have been some detailed posts here about the 401, so you can learn a lot just searching for those. My real concern would be the pattern dials and how freely they move. If the machine sat around for a long time and the oil gunked up in the pattern cams, it can be a bit of work to get everything moving again.
I don't quilt, so I don't know how well the 401 works for that.