Machine type
Machines that sew a straight stitch and nothing else, which is all many quilters and dressmakers want. That covers Singer's Featherweight and 301, the potted-motor 15-91 and 201-2, the three-quarter-size 99K and the White Rotary family. They're simple and sturdy. What goes wrong is usually old oil and grease, perished wiring and a missing bobbin case, and each one takes its own bobbin, so check it's the right one.
6 models we cover.

Singer
Straight stitch$470–$1,000 typical ask
198 on eBay
Singer
Straight stitch$290–$450 typical ask
113 on eBay
Singer
Straight stitch$240–$450 typical ask
112 on eBay
Singer
Straight stitch$390–$1,100 typical ask
66 on eBay
Singer
Straight stitch$160–$270 typical ask
121 on eBay
White
Straight stitch$170–$625 typical ask
124 on eBay