I went over to the akparts website and looked around a little. Let's take a look at the $269 A3 upper for reference. There are a few things that jumped right out at me...
The barrels are 4140 steel, most of the quality AR barrels are 4150 steel. It's a little harder and a better barrel steel. (Add $25)
Their barrels aren't chrome lined. That's a subject that causes some concern amongst riflemen, but most hard core AR shooters want chrome lined barrels and chambers. (Add $50)
Another thing I see is that it is "less the bolt and carrier assembly and charging handle". That's the heart of the rifle. It can't shoot without the bolt and carrier. (Add $150)
This is for the A3 flattop. If you want to add a removable carry handle, add another $100.
Now you have added $225 worth of upgrades to the upper and for that $495 or a little more, you can have a top quality upper form a known and reputable manufacturer.