Try buying NOS pair of KT66 or EL34... $300 for a pair would sound like a bargain!
Yup, a pair of Philips XF2 EL34 should only cost $2-250, I have seen clear glass GEC KT66 for $250 a pair. But smoked glass GEC KT66 and metal base Philips EL34 will run you $500, even more for GEC KT77 if you can find a NOS pair. Several markets for these tubes, two-channel stereo amps, guitar amps, and now headphone amps, so demand is very high! Gotta pay for the best I'm afraid.