Will be connected to my FIREBOX for monitoring...

is 50$ a sane budget?

are there decent headphones which are relatively cheap?
You know what man believe it or not... and trust me I hate behringer products... but the behringer studio headphones I love. They are only 20 bucks... They sound better than any headphones in that price range and are studio quality. i've used them in a ton of recordings and they have been really reliable. they also have the looks and feel of your more expensive studio headphones. I'd grab a pair for 20 bucks... I mean someone could make the argument that they aren't the best but everything sounds so clear in them it's def good enough for me and for 20 bucks you can't beat it.
I have some Samson ones that are pretty damn good. Not sure on the US price of them but I got them for £15 reduced from £50. Flattest response I've heard.