Lower end pre builts, you might be able to match the prices, But when you build your own, your wanting speed,reliability,clear performance. If you dont do Intensive stuff on a computer, then a 400$ HP or Dell will be fine. But keep in mind, the Motherboards and PSU in them are very cheaply made with small 12v rails which are known to popping resistors and or damaging everything plugged into the motherboard.
And thats where pre builts get you. You buy their ready to go out the box, but you have to upgrade ram and add in a gfx card so your not using the onboard one. In the end you done added 200-300 more dollars.