How expensive are best NOS tubes ? And how difficult to find ?

Speaking of 6922 tubes, try some  National Matsushita 7DJ8/PCC88 made in Japan new manufacture. The have replaced my Valvo Cca's sound great and are very affordable.

Very new to this game, just purchased my first tube pre amp. Been ss forever. My question is, what is the difference in plates on a tube? My pre calls for a 12au7 long plate. Are there any other "plates"?

The plates are the black or gray (usually gray) rectangular or square objects that take up most of the space in the tube. Long plates are usually found in older tubes, early (1950s) versions of tubes like the 12AU7. They may sound different from the later short plate or box plate or square plate (three different names for the same type of plate) versions of the tube but any 12AU7 socket that can use a long plate should also be able to use a short plate.

Tell us what brand of preamp you have and we may be able to help you get the right tubes in it.

Just purchased a Rogue Pharaoh integrated and am not familiar with tube jargon but read that "rolling" tube can be fun experiment if you know what you're doing. 

Welcome to the world of tubes.  The Rogue should be a nice sounding integrated.  I know we have some Rogue fans here.

Tube rolling is just trying different tube brands in your amp to tune the sound to your liking.  There are also variations on the 12AU7 like the 5814 and many others that work where a 12AU7 is called for.   So there are a lot of tubes that you can roll into your amp, but it's not a cheap form of entertainment.  The Rogue has 2 12AU7s from what I can tell and any 12AU7 should be able to work in your amp.  What brand of tubes did it come with? 

Why don't you start a new thread asking Rogue owners what tube brands they found to work well  in their amps.  They can probably give you a better educated opinion than I can.