Almarg has good advice and Tvad and Tzh21y list some names. The only sure-fire way to "know" the history of prices and get a feeling for where items trade is to get a subscription to the Audiogon BlueBook, to understand that it only works for relatively liquidly-traded items, and to understand that it does not work.
The other way to get good equipment at prices which will not cause you to lose too much money if and when you sell it is to buy what I would call "soon to be but not yet classic" gear at 20-30cts on the original dollar. I have bought some 20-30yr old equipment at that kind of prices, and all the well-regarded pieces I have bought have been real prizes. Sometimes really excellent equipment just loses its fan appeal, drifts down to that kind of price after a decade or two, and then it represents absolutely fantastic value for money.
The other way to get good equipment at prices which will not cause you to lose too much money if and when you sell it is to buy what I would call "soon to be but not yet classic" gear at 20-30cts on the original dollar. I have bought some 20-30yr old equipment at that kind of prices, and all the well-regarded pieces I have bought have been real prizes. Sometimes really excellent equipment just loses its fan appeal, drifts down to that kind of price after a decade or two, and then it represents absolutely fantastic value for money.