i'm using my goldring DR150s with a headstage lyrix amp... costs around 150$, works very well, bass and details improved.... you should find some review by headphoneaddict about this amp, otherwise just send him a pm, he's very friendly and helpful...
I use Shellbrook Audio Ascent Signature amp for my DR150 which is basically maxxed out Pimeta home amp version. If you can purchase any Pimeta home amp used in F/S section, you will most likely be under your budget. There are lots of newer amps out there but usually much more expensive than your budget allowed. The Pimeta is older design amp but sounds wonderful with my DR150. Good luck.
Just got some DR150s (brand new £30 delivered from play.com - at that price it's time for a new Goldring fad). Very amp sensitive. Tried them out with a old Sony AV amp, a FiiO e5 and a Juice 2214 CMOY and there are very discernable differences between them.
The CMOY seems to give the most controlled perfomance but I'm guessing that ther's room for improvement. I'm quite surprised because the Sony does a lot better with my Goldring NS1000s. Have seen people recommending allsorts amp wise. Someone mentioned in another thread that the DR150s pair well with the very cheap Behringer AMP800. Any other recommendations at the affordable end? Would seem a little weird to pair a £30 set of headphones with an expensive amp.