The Singer model 66 is a good solid stout machine but it is not an industrial by any means.
The early ones used a round knob to control the stitch length. It has no reference marks. The later ones had a stitch length lever with reference marks and a back tacker.
It uses the Class 66 steel bobbins. They are quite common. You can find them most anywhere.
It uses the common 15x1 needle.
It uses the regular low shank feet avail lots of places.
Advantages, beats me, I have 5 of them. 2 treadles, 3 electric. They sew beautiful straight stitches.
They are very durable and trouble free. Just feed 'em some oil and they're happy.
I really can't think of any fragile or troublesome parts to them.
Since you can't test run it I'd check it to be sure it's free turning, then check the wiring and if all is well I think I'd try to get it for $25.00 or so.
JMHO
Joe