If you're on a super budget go for the Neu HX-6000. Available only from Japan online, but those babies punch far, FAR above their pricepoint at $30 and to me far surpassing every mod of the HP-100 I've heard yet. Flatter F.R., more natural / lifelike sound for faithful reproduction and crisp details but without that hyper-resolving / fatiguing quality existing in the HP-100, 150/151 and especially their newest HP-1000 which to me was among the worst headphones I've ever heard; and that includes two separate pairs and on 4 separate systems. The HP-150 does have a somewhat more realistic F.R. (darker), but for me after 5 years toying with various mods of these I've closed the door on SoundMagic. Mods help somewhat to darken the sound and tighten the bass but especially when comparing them to serious contenders I realize it's still somewhat piercing on top with inadequate sub-bass; the 150 having more but still rolled off.
The HX-6000 retain the same tonality of the HP-150's but with better texture and bass that reaches deeper. Though not needed, these also benefit from an internal mod (cotton damping pads) and ferrite beads on the cable. It's a somewhat clinical sound though so for me I rely on them as studio monitors for mixing.
Also consider the Sennheiser HD-380 pro for a little more if you like good bass quality and moderate detail. The bass on that thing is not even in the same galaxy as a modded HP-150, the 380 has shown me EXACTLY what I've been missing in the bass department over the years and it's astonishing the level of bass detail that simply does not exist at all on any of the SoundMagics. Not that the S.M. don't have any bass, but you'll hear a night/day difference between the two and never go back. It sounds harsh but believe me I speak from 5 years with their models and connected to about 15 different systems. Also consider Fostex TH-900 and a used Sennheiser HD-250 or 300.