If anything, I'd just buy the 701s. Even though they 'need an amp' to really get the sound out of them, you still can listen and find enjoyment for them until you have the money to get the amp later on down the line.
My philosophy is to go for that top tier quality you can afford the first time around, because you may get the cheaper pair now and then feel an itching for more after reading about how such and such headphones are in another class than what you have... So instead of eventually getting the 701s for $250, you just spent extra money playing around with some other headphones.
Headphones in the class of the K701s, HD600/650s, and RS1s are pretty much the top level of 'affordable consumer class' headphones. There isn't really a jump up in headphones unless you're willing to spend a lot more. The difference in this class is ultimately the different sound signatures the headphones present. These headphones are amazingly scalable, so you can dump a fortune into them before you ever 'max them out.' For example, the B-52, a $5,000+ amp, was voiced with the HD600s.
Just get the 701s now, bear with the somewhat diminished sound and get the amp later.