First question; who is selling these tubes and quoting the prices? Only buy from reputable dealers.
So, I assume you are looking to buy NOS tubes rather than new production. There are so many brands and variations. There are different variants of Tung-Sol, you need to know which version you are buying. One TS oval plate will cost over $300, it's a rare tube from the 1940s and one of the greatest tubes of all time. There are also NOS TS tubes for $50 each.
http://www.schiit.com/about/news/octal-lisst-new-tube-options
Why buy a LISST tube? Then your preamp would be all solid state.
So, I assume you are looking to buy NOS tubes rather than new production. There are so many brands and variations. There are different variants of Tung-Sol, you need to know which version you are buying. One TS oval plate will cost over $300, it's a rare tube from the 1940s and one of the greatest tubes of all time. There are also NOS TS tubes for $50 each.
http://www.schiit.com/about/news/octal-lisst-new-tube-options
Why buy a LISST tube? Then your preamp would be all solid state.