I am in the business and if your calling 400 - 500 mid where do you get your parts? Entry Motherboard 100 to 150. Cheepo case 45.00, Small Hard Drive 45.00, Entry Level Graphics Card 80.00, Low wattage power supply, 50.00, Slow memory 35.00 (2gb) DVD burner 22.00 Total for the this 377.00 without OS.
I was making this estimate on a small off chance he was building it. But for prebuilt, I admit 400-500 is low end. However for my "mid-range" PC that is do-it-yourself:
I use Newegg/Officemax (Only gotten HDD from there), my system which runs from Aces High (max settings) to Crysis (Low/Med) just fine was about 550$. Not low end, and by no means high end. AMD, GeForce 7900, 2GB DDR2-800 Ram, 630watt (20+A on 12V rail) PSU.
Mobo 50$ CPU 60$ RAM 40$ GPU 100$ PSU 35$ HDDs (160/320GB) 55/85$ Case 55$ DVD 32$ Total: 512$ Approx.
True it is not the greatest, but it runs stable and no troubles at all.
However for a Shelf PC, I leave that to the rest to explain. The E-machines I use to have ran it fine, was better with even a cruddy add-on GPU (GeForce 7100). However, it has been a while since I looked at Shelf PCs