MacBook Pro Headphone Out sufficient?

I happen to own both a pair of IEMs and a Macbook Pro from 2009. The SQ really surprised me, I thought it was downright horrendous... Fortunately with a good DAC/Amp you don't have to worry about that. The first thing I can think of is the Apogee duet, which is outside your range unless maybe you find a used one, but I hear extremely good things about it and it seems like it's basically the DAC/Amp to get at that price range for a mac (I'm sorry this is all the help I could provide, I haven't honestly experienced anything that cheap, since I only recently started using my computer as a source).

You really want to look in the Dedicated Source Components forum, there's a load of affordable DACs in threads there, shouldn't even need to do a search. The Yulong D100 is more or less what I've decided I want to hook up to my Mac Min but w/shipping that's really a $500 product so outside your budget. 

If you do decide to use the laptop, you might want to look into a good ground loop isolater. Most devices with higher levels of sensitivity will get lots of noise and stuff if the laptop happens to be plugged in to charge while you use it, or even if you use an USB powered DAC.

Good ones can be had for around 50$ and isolate the audio line going out, you can get cheap ones that hook up to the laptop's power plug and basically remove the ground line, but that's not a good idea.

Keep in mind that the Macbook Pro's all have one of those combined analog/optical digital outputs, so the world of DAC's opens up quite a bit.  you don't have to use USB all the time!  I just picked up a Zero DAC/Amp in the for sale forums here for a heck of a deal, and am using it that way on my iMac (optical out).  As with anything, ymmv, so be sure to shop around a bit.