Is it common for tubes to outweigh the cost of the amp or preamp?

I just got my first tube (headphone) amp and was wondering if it is common to spend more on the tubes than the actual cost of the amp. The amp was $599 with stock tubes. I just ordered NOS driver tubes that ran $640 for the pair and the power tube upgrade I'm planning will be another $300. That has the tubes sitting at 1.5 times the cost of the amp itself.

I don't find the total of $1539 for the amp and upgraded tubes unreasonable but considering the next model (amp) up is $1199, it has me wondering what would be better... a lower cost amp with superior tubes or a higher cost amp with stock tubes?