I've been using the Russian 6n23p-ev, the upgraded military/industrial version of the tubes supplied with kit. Whether they are actually a better tube than the standard 6n23p I don't know, but they sound a lot better to my ears.
Parts Connexion sell matched pairs for $55. If you're not already signed up to their email newsletters, you can sign up & get a $25 store credit, so you could get a pair for $30.
Btw, I also have some 7308 & Telefunken E88CC gold pin, and I don't feel the 6n23p-ev is far behind, but YMMV....