HP is currently selling the Pavilion a1030e and a1000y desktop systems which only cost $249 after a $50 rebate. The a1030e ships with a Sempron 3000+, 40GB HDD and 256MB memory while the a1000y comes with an Intel Celeron processor.
A display isn't included but consumers why go for a 15-inch LCD display can get a free upgrade to a 17-inch one after adding more memory of upgrading other features. This is a $50 discount.
Mainstream computer prices have been falling to $399 and notebook prices are also dropping as HP and Acer each shipped $499 notebooks last month. More notebooks at this price range can be expected soon in the back-to-school period in September. More details at CNET