I put together a 105 build kit myself by ordering the various parts from different online vendors. I first made a list of the parts I wanted before shopping and then compared all of the individual prices on a spreadsheet.

I took into account shipping costs, discount coupons, seasonal sales, and taxes to come up with the least expensive kit to upgrade my wife's bike. Some was purchased from here and others from there. But they all started to arrive at about the same time.