eMachines offers only a handful of models at any one time, and the top-of-the-line T6420 is only $599. Despite the rock-bottom price, you can squeeze a lot of value from one of these PCs, thanks to decent upgrade opportunities, such as x16 PCIe slots.
Interestingly, the systems are all AMD based, and potential buyers should stick to the two more expensive models, skipping the underpowered Sempron processors. For example, the T6216 is only $50 more than the T3410, and the former kicks the CPU up to an Athlon, which is key.
The specific model numbers and configurations change on a fairly regular basis, sometimes even downgrading slightly, as in the case of the T6420 vs. last year's T6520.