If you build it yourself, you will find in most cases, that the cost will be similar to say Dell or in some cases a bit higher.
However, you can select the parts best suited for your budget and uses. And if you want, go top of the line parts.
You also select the style of case you want and there are many to pick from, most with multiple cd bays, floppy bay,
multiple internal hard drive bays ... and you get to chose if you want an AMD or INTEL CPU as you will also be
selecting your own motherboard ... only downside is how long it will take you to get all the software installed and
configured. For the cpu, follow the instruction sheet exactly as to how to handle it and mount the fan / heatsink
as that is the most critical part. Check the pins are nice and straight before attempting to insert into the socket.
A mechanical pencil works very well to straighten any bent pins.
Let us know how you do. It should take about 2 days at most once you have all the parts.