As I've found out recently, the amount you spend does not always equate to the level of sound quality. When I first started out a couple months ago, I wanted the "best" for a certain price range. I ended up getting the Sennheiser HD700 ($1000) and then later a Woo Audio WA7 amp/DAC combo (also $1000). For $2000 the sound was good for sure, and it sits at home as my home setup. I just recently finished my work setup at about half the price of $1000, and it's a good 30-40% better than my home setup at half the price.
My work setup is Firestone Audio Spitfire HD DAC -> Bottlehead Crack amp -> Beyerdynamic T90 headphones. Also have the Speedball upgrade for the Crack, haven't installed yet.
A couple words of advice:
Wait for a sale for everything!
When I started out, I bought the HD598 for full price of $250. Then I bought the HD700 at $1000. Now I see the HD700 on sale for as low as $750 quite frequently. The Beyerdynamic T90 is normally $650, but I bought it on sale at $500. The Bottlehead Crack is $280 but I bought it during a promotion where they were giving away the Speedball upgrade ($120 value) for free. The Spitfire DAC is normally $300, but I bought it for $200. It's a decent DAC, but I got it for having both USB and optical. Plenty of decent DACs even cheaper if you only need USB. Schiit Modi at $100, ODAC at $150. So for under $1000, I bought a $1350 setup.
DIY if you can
I heard great things about the Bottlehead Crack early on, but was hesitant to get own hands dirty into soldering. I finally pulled the trigger when they had a weekend sale that included the Speedball upgrade for free. The guide that came with the kit was really easy to follow. I've had a little experience on soldering in the past, but really anyone can do it with the guide. I got it all working on the first try too. And for about a quarter of the price of the WA7, I can say it is definitely on par, if not better sonically. It really makes you realize how much markup is added for labor, professional construction, and aesthetic exterior design on products. Note that the Crack only works well with higher impedance headphones (>120 ohm).
Right pairings can really shine
Amps and headphones are really one of those things where the phrase "the whole is greater than the sum of its parts" can really apply. When I first got the T90 headphones, I haven't built the Crack yet. I compared it to the HD700 and I thought the HD700 was better. But when I paired the T90 with the Crack, it was out of this world. I also tried the HD700 with the Crack, but to my surprise, it didn't really get an improvement. In fact, I like the sound of the HD700 from the WA7 more. Both are above 120 ohms impedance: T90 at 250 ohms and HD700 at 150 ohms, so they both work within the Crack's specifications. Still the combination of Crack and T90 is way better than Crack and HD700 to me, and even better than WA7 and HD700. And this is without the Speedball installed. You can read more about my experience with this pairing here: http://www.head-fi.org/t/607079/beyerdynamic-t90-d/930#post_9780801