Scott;1st always use the KISS approach to any project or deal, the more complicated you make it there more complicated it will be.I have built for investors, custom homes and specs, all different in there outcome of how profit ended up.Get three bids with their schedules and there plans, this will give you an average, call there references, I mean previous homeowners that the bidders built for, pick up the phone and call some trade’s, the construction business is a small world all the trades/suppliers worked or knows somebody that have worked for the GCs.As for what to payout would be, my rule of thumb is, cost to build x 25%, the 25% covers my overhead, taxes, legal fees, mister Murphy ECT, then I verify that number with a CMA from a Real estate Broker, if numbers line up then where good if not the adjustments will be needed.

That being said, smaller local suppliers can beat them on service if they are good.

I found the deal through SIDRAN wealth a turn key supplier that develops homes in secondary markets.

Contractors want to buy the materials because we have relationships with quality suppliers.

I interviewed several solar companies before I went with Revolusun in Burlington MA.Mass electric announced rates to go up again because the suppliers providing power to national grid rates when up. 

Jay, great suggestion, have been using this product "Chinese Granite" for almost 5 years now, unfortunatley the supplier has now begun to discontinue it and only carry the 3cm :( Still get some really cheap colors if you need, but the Chinese granite was literally a steal.

Another angle to get info is to find the local chemical suppliers.

You need to find a semi local supplier of used machines.

I've done one deal with NWA down here in San Antonio and to summarize, they're a wholesaler (read property supplier).

Go to a supplier of the products for each scope of the job.