Tubes for my Mac's 275....NOS or just used?

I have purchased tubes before (from Andy) etc. and I do understand the meaning of NOS. However, a big thank you from me for your help.
I would like try to keep the cost down so I though going to e-bay may be good.
If I do, sightly used is OK? I would also think so...right?
Any of you have success with anyone in particular on e-bay? In other words...are there any regular tube dealers on e-bay.

P.S. Neil, I am getting there...(slowly).

Thanks Albert...in particular what should I be looking for in a used (or even NOS) tube Telefunken?

Please, all respond if you can offer advice.

Tks!

Rick (RWD)