Tesla Tubes

There is no guarantee that NOS= Old but never used, or just Old stock tubes will sound better.
The gold pins are as Swampwalker says and I might add supposedly better tubes all around. Also the diamond between the pins on the bottom indicate made by Telefunken.
I became a big fan of rolling tubes (changing them to another brand even type) after hearing how much better my first tube amp sounded with tubes manufactured in the 1940s, 50s and 60s.
So if your willing to hear sound with no or only moderate improvement for you money you might want to try it.
Be sure that you are buying one of 2 possibilities . The first that you are getting tubes from Tesla made before 1980or
Currently manufactured tubes made by a company sometimes called JJ Tesla. They are JJs which are good tubes but you can buy them for very reasonable prices, if you search the "interweb". I find an outfit called Eurotubes does a very good job with JJs and ships very quickly. I have no association with them at all financial or otherwise.
BTW which tube type are you hoping to buy?

Be aware that some circuits really respond to tube rolling while others don't. My own experience with ARC left me thinking they are not for the tube roller (input and small signal tubes).
A fair price is difficult to know, several factors go into the asking price, generally how well the tube tests is a big factor but prices are a moving target. In general prices for these tubes are climbing as they are getting used up, and I think people are more aware of tube audio.. The ECC83 or 12AX7 is a popular tube. The Mullard and Telefunken will command a higher price depending on condition and variant, than the GE. You really have to check around. Visit sites like Brent Jesse to get oriented. It doesn't hurt to watch the tubes for sale on this site for a bit, to get a sense of what the used tube market is like.
Be aware that many tube sellers are not all that well informed themselves and terms like NOS are used loosely by some. Buying old tubes is not like buying gear from a manufacturer, but some well established sellers will warrant what they sell.