Value is subjective. I think they're becoming over priced just like Featherweights. Vintage sewing machine prices in general are getting out of control. 301s are still very common. Lots of them out there. Nothing rare or "special" about them other than they sew very well just like millions of other vintage machines. The only way I would pay $100 or more for one is if it was still in the original crate, never been touched. I've had 4 of them, never paid more than $40 and that was for a very low serial number, one of the first 10,000 produced black short bed machines in a #40 cabinet. One was given to me.
All that being said, I do enjoy sewing with a 301 but I'm not really a Singer gal. I usually prefer my Japanese machines.
Cari