I would buy the new ones.
They have a much better graphics card and much better wattage consumption. If you have it as HTPC you will probably leave it almost always on, so you will save some $ on electric bills.
I'm already going $200 over budget, I don't wanna go over another $100.
Plus, the computer won't be very bloated, so I'll leave it off and turn it on in 20 seconds.