If you don't have an amp, you don't want to go much about $200-$300 or you won't be getting the best sound possible.
A commonly recommend amp in this thread that is versatile and basshead-worthy is the Cayin C5.
I'll quote myself from a couple pages back first (this is roughly in escalating price and basshead performance). These are headphones I'd be down with no EQ on:
The Audio-Technica WS99 hit hard and have a V shaped signature. The earpads aren't terribly big. Some people recommend the Brainwavz HM5 pads for these, but they seemed to leak sound for me. The new HM5 Angled pads might not leak sound with them (they're a little narrower), but they weren't out when I had these headphones.
The V-Moda Crossfade M-100 sound good and hit hard. Also V shaped sound. They have XL pads that are mandatory for comfort. If you have particularly large ears, they still won't fit.
The AudioQuest Nighthawk are quite solid and do not cause any fatigue at all over extended periods. I feel like they benefit from but don't require a decent amp. They're pretty darn expensive, though. Semi-open, so they don't isolate a ton.
Fostex TH600 (then TH900) are amazing but cost a lot and need a good amp to pair with. You probably don't want to start here because of diminishing returns. Semi-closed, so they don't isolate a ton.