But, I personally wouldn't buy most '70's A's even if they were only $50! Now '40s and '50s, that's another thing.
agreed. basically 60's and 70's A Zildjians are inexpensive because there are a lot of them out there, and there are a lot of duds.
once rock and roll became popular, zildjian rides turned into manhole covers. IMHO 20" A Zildjians sound best in the 1800-2000 gram range. but once rock became popular, they beefed up to 2400+ grams. i've even seen some that are in the 2800 gram range.
plus, most ebay sellers don't weigh the cymbals or give any description. so i'm not willing to risk $100 on what could be a crap cymbal.
the ones that do have weights and good descriptions will sell for a little more. especially if they are in that prime thin to medium-thin weight range. but even those won't command the same high price of a trans stamp, small stamp or block stamp because there are so many of them out there, and they don't have the same complexity that you find in pre-1960's zildjians.
are they good cymbals? sure (depending on your needs). are they a dime a dozen? yep.