10 years ago is not that much in the headphone world. It’s not a market where there is that much demand. Very different from the current iem market. A 200 pound headphone from 10 years ago will be superior to a cheap headphone from today generally speaking. Build quality is definitely also a factor which, if anything, has gotten more expensive to do well. The best deals to be had on headphones would be second hand ones. Especially less known brands, but even sennheiser headphones can be had for absolute deals. I paid like 70 euros for my hd560s. A sundara is around 200 euros, a hd700 goes for like 300-400 euros and is (IMO) basically 80% of an hd800. Speaking of which, I got my hd800s for 800 euros and you can find the normal hd800 for around 600-700. Keep in mind that these are all headphones that are still considered very competitive at their new price points which is on average around twice the secondhand price. I would argue that for iems the secondhand market doesn’t make that much sense unless you can find modern products for good deals. Especially when many companies do such aggressive discounts so often.