I would not buy a low end Singer - having done it myself. Because if your friends ever want to start quilting then this will only frustrate them. The dogs are spaced too far apart for picking up the fabric for 1/4" seams as well as too far back to sew right from the edge. It just isn't versatile enough to do different types of sewing. So I would avoid at all costs and think a better, older machine second hand would serve them much better.Maybe that's why I struggled with my quarter inch seams. I see a lot of Janomes and Berninas recommended in the comments. I'm surprised not to see a Pfaff recommended because I've seen several reports of people very happy with their Pfaffs.
I think I'll have to spend a day sometime just trying out various brands and models. I'm glad I have this experience with my low-end Singer, though, so I'll at least have something to compare.