John, I tend to break them before even coming close to wearing a blade out. Once I have at least 24 broken in hand I can justify buying a blade welder.
However, until then, I've been buying the least expensive Enco has; the Flex Back Carbon Steel in 10, 14 & 18 TPI. I don't saw real thin sheet metal very often so that is why I will only keep one 18 tooth on hand to several of each of the 10 & 14.
The trick to making the El Cheapos last is to run them slow, keep them cutting - don't let them "rub".