If you find WE Nos 300B to be too expensive, then I recommend you try
Psavne Acme 300B.
https://www.hifi-amplifiers.com/en/psvane-acme-serie-300b-hiend-vacuum-tube-replace-we300b-matched-pair-p-5262.html
I had have sweet and natural sound with Line Magnetic 508 with Acme 300B for more than 400 hours running.
My Nos WE 300B had been running more than 10K hours with no problem.
If you account for its longevity, then it is not expensive.
The problem is that it is hard to get good and genuine Nos 300B at reasonable price.
Psavne Acme 300B.
https://www.hifi-amplifiers.com/en/psvane-acme-serie-300b-hiend-vacuum-tube-replace-we300b-matched-pair-p-5262.html
I had have sweet and natural sound with Line Magnetic 508 with Acme 300B for more than 400 hours running.
My Nos WE 300B had been running more than 10K hours with no problem.
If you account for its longevity, then it is not expensive.
The problem is that it is hard to get good and genuine Nos 300B at reasonable price.