Well, Sushi, I agree with you about the even vs. odd ordered harmonics, but as to the rest, I don't figure I know all there is to know about why one amp sounds better than another. As to prices, yes, there are some super expensive tube amps out there, as there are some super expensive pressed sand amps.
Back in the golden-age of tube amps (early to mid 60's) a really nice house cost $40,000, a loaded Chevy Impala with a big V8 could be had for a bit over $3,000, a Buick for about $4,000 and a Cadillac for $5-6,000. So, basically a bit over 10 cents in 1960 dollars, will buy you about what a 2003 dollar will buy you. So, a top of the line tube amp in 1960 might have gone for as much as $500 back then, a perfect example would probably go for thousands of dollars today, used.
There are some super values in SET tube amps. Check out the Antique Sound Labs line. They sound sweet. They don't cost an arm and a leg. Do some research on the net, and you'll find some other good buys on great sounding tube amps.
