Don't be so sure.
Custom made computers are only popular among gamers and hardcore users who know what they want. While there is a distinct difference between "2 Terrabyte Hard Drive" and "It stores a lot" to a techie, the layperson will only be able to comprehend the latter, and is all they need to hear from the salesperson at Best Buy before they make the purchase.
As it is, those who could truly make use of a custom-built computer are savvy enough to either do it themselves or know who to go to to get it done.
As an inquisitive techie myself, I would rather get somebody to show me how to do it, rather than just paying someone to do it.
As such, I would only value it at mid $xxx at best. It's bound to drive some traffic, but don't expect to get rich off this name.