I did the math a while ago. It was cheaper for me to buy a case of tubes and match my own than it is to buy matched sets over the lifespans of the amps. I'm not terribly picky with the brands of tubes, so I've been collecting mostly old Russian NEVZ, Reflektor, and Voskhod stuff with a few batches of US JAN GE thrown in for good measure.
Maybe not so much of a savings when talking about rectifier tubes, but considering they are typically quicker to burn out than the driver and pre-amp tubes, I said screw it and ordered. Worst case, I'm out a bit of money and am soldering some rectifier diodes together along with thermistors on octal bases. :)