Id get Sony mdr-xb series headphone (xb300 or higher) The thing is they are nor very acurate so when you get more money get sennheiser 280 hd or better for flat frenquencies respond .I use both of them . I relate on the mdr xb300 for the heavy bass and mix on sennheiser hd360 pro for the flat sound . With sony mdr you cant go wrong . The xb is for extreme bass so if you need headphone with alot of bass that what you need . Im sure you can find some for under 50 $ (paid mine 50 $ a few years ago ) . Maybe you already know but it is not recommend to mix on headphone only so its always good to relate on speaker see how you mix sound on them .
Hope it help .