Out of interest what equipment do you use when listening to your phones, what are your phones plugged into? Depending on your kit you might get a better improvement with a proper headphone amp or a combined dac/headphone amp.
I have the SR80i Grados which were originally plugged straight into my pc's headphone socket. I have a decent sound card in my pc (Creative X-Fi) and the Grados sounded pretty good but a bit restrained. I then tried my phones on my dads Marantz amp and the phones sounded better, more detailed and clearer than using my pc's headphone socket. My dad has a pair of the older SR60 phones and I was a bit shocked when my new SR80i's didn't sound anywhere near as good via my pc.
So my pc setup was really holding back the true performance of my SR80i's, I was advised on here to look for a proper dac/headphone amp and after lots of questions and a fair bit of research ended up buying this
little box of goodness. My headphones now sound fantastic with a huge increase in sound quality over my old pc setup. My phones sounded good via the Marantz but sound even better via the little box of tricks.
I bought the Fubar at the beginning of the year when it was on special offer for around £120 ish, I think there are a few options with your budget especially if you consider second hand.
idc is our resident headphone expert so he might be able to advise something suitable within budget.