The ATH-50M sometimes go on sale for around €100 (the non-X model). I see a pair of brand-new ones for €119 shipped on ebay right but that’s still more than your budget. They’re very solid as far as affordable studio headphones go.
I hesitate to recommend something that I haven’t used myself, but the Superlux HD 681 are frequently recommended as cheap studio headphones that are much better than the price indicates (one of those Chinese knockoff products that have surprising quality, like with some mics). Perhaps worth looking into!
For hifi headphones, I’m currently in love with the Ultrasone HFI 15G that are wonderful for €70. I only picked those up for using them with a Playstation Vita, but the sound quality surprised me. Those are not studio headphones, though, just for pleasure.
edit: I should’ve read the entire thread!