Between $20 and $25 is a good price to pay. I bought my first slim adjustable for $13 on E-bay several weeks ago, but I was a bit lucky (http://badgerandblade.com/vb/showth...han-40-years?p=4215413&highlight=#post4215413 ). The E-bay photos were a bit fuzzy and the accompanying description had very little detail. It turned out to be a good razor with no defects. It's a great razor. Good luck with it.
A fair price. I just sold one on the bay for $40 a month or two ago. I would say $25 to $30 is a decent price if it is in good shape. They seldom go for less than that these days.
My slim cost me my Grandfather. He passed in 1972 and I got his 1962 Slim. I shaved with it for the first time yesterday. That would be the first time in 40 years that razor has been used and it's only been used by 2 people. Me and my Grandfather.
I just paid $35 (shipping included) for a very clean birth quarter Slim (K-2). I don't know ANYTHING about vintage double edges, but I bought it from a B&B member and I think it was fair.