It would be nice to have something where it searches pre built systems with 'specs like this'.

Sometimes it is cheaper to buy a pre built system with all (or most) of the right parts than it is to build it yourself.

Another option would be to let users spec out the system and then let manufacturers bid on delivering a system with those or similar specs.

A manufacturer that buys parts wholesale will be able to give a significant price reduction over buying all of the parts on ebay or amazon or egghead. (And any parts they have sitting around are just wasted capital, so they want to move parts as long as they can make money on them... you could even let them sell excess parts).

You could take a cut of the money saved through the bid process/whoesaling.