Some Thoughts Based on almost 40 Years of Listening
The initial posts here are outstanding.
I would add that in my sixty years, I have probably been a serious listener for almost 40. During that time, I have had about six sets of headphones that I have relied upon for my serious classical listening. (I used to be a professional musician, used the proceeds from that to pay for college and my advanced degrees and then I worked and taught outside music before retiring last year.)
My rule has been to listen to headphones and buy the best one I can afford at the time, at the point where the sound quality begins to really diminish for the price being charged. An example would be the recent purchase of a set of Grado SR-225's that I made. I was able to buy them for about $5 more than the retail on the 125's so I did. That is clearly the line in the series where the sound becomes true and balanced throughout the entire spectrum and where improvements come but at a very high cost.
Previous headphones I selected included a splendid set of AKG's purchased in Hong Kong in 1987 (back then, the dollar was worth a lot and bought a great deal especially when one was able to bargain in the local language or had friends who could intercede for you) which lasted darn near forever, but the rule I used was the same, buy at the point where you began to pay dearly for slight improvements.
Hope this helps you preserve your hard earned funds, especially in these tough times.
Cheers,