Why the Cheapest Isn't Cheap
When assessing cost, buying for value is more important than low initial purchase price. Always buying the 'on sale' product will produce a computer network that is difficult to maintain because the tools and experience gained on one computer can't be transferred to the other computers because they are different brands, or models. Standardization of hardware and installed software (the same versions of Office for example) offers great benefits in knowledge for both the technical support side, but for users who can exchange information on how to more efficiently use the products.

Inexpensive (Cheap) Hardware is S-l-o-w
By cheap, I am talking about the very bottom priced hardware. There is a reason that it's cheaper and slower. It's using technology that is three to five years old. No, I am not kidding.

I have a customer who told me "We only do word processing and spreadsheets. The very cheapest computers are good enough for us". This is the same customer who turned off the anti-virus software (See the Security page) because it was slowing his computer down! He paid me to remove the very nasty virus that he acquired while it was turned off. True story.

Slow hardware affects every single thing done on a computer for it's entire life cycle, and indeed shortens it's life cycle, because as new versions of software require more speed and memory, the cheap box can't handle the new products and has to be replaced in three years instead of four to five.

My Recommendations
Build it yourself computers were once cost effective, but as the economies of scale have kicked in, the build it yourself computer is more expensive and less reliable than the one from the reputable manufacturers. And the build it your-self computer probably doesn't have a warranty.

Pick a brand that you are comfortable with and standardize on a model/feature set. In the old days they used to say "Nobody ever got fired for buying IBM". Now I say no body ever got fired for buying a Pentium P4. Minimum of 1/2 Gigabytes of memory. I personally buy a couple of steps down from the fastest in the family.

Yes, I have a particular brand that I favor, but you'll have to ask me in person to find that out.