Lara122,
If the machine is in good working order, and the cabinet is also in good condition $50.00 isn't too much. The more accessories and attachments that come with it the better.
The red eye model 66 is no different mechanically than any other model 66 of similar vintage. But it is a well liked design and it was only made up until 1927 I think. So although it's not super rare, it's not super common either.
I have two, both treadles. I'd gladly adopt another if it comes along.
Joe