If you already have a decent speaker amp/receiver (particularly with unused 2nd room taps), get an HE-6 and hook it up to the speaker taps. It's one of the best headphones at any price and will consume your entire budget (exactly), but you'll be firmly in Summit-fi and never look back.
If your speaker amp puts out over 90 wpc, HiFiMAN also sells a customized resistor box for $99 called an HE-Adapter that will "protect amplifiers and headphones when using a speaker amplifier to drive HE-6". Even if your amp is more modest, the adapter would simplify the hookup and eliminate the need for a speaker tap adapter cable. But the first time I hooked my HE-6 to speaker taps, I just chopped up the SE adapter that came with it (the HE-6 is one of the very few headphones that come with a 4-pin XLR plug stock, much like the AKG K1000; it's like a clue that they need speaker amp power).
I rotate between four Summit-fi headphones and the HE-6 is the one that seems to stay on my head the longest. There's a couple of good threads on it and it's amplification requirements, which are quite unusual. I drive mine with a ~$175 45 wpc SS speaker amp and a $2k tube preamp, but the HE-6 sounds great without the preamp as well, straight out of the RA150.
Edited by grokit - 8/9/12 at 4:17am