If you want to know prices of granite go to a granite supplier and ask what their cost per sq ft is for different selections.

If you have a large project where many material suppliers are involved, you ask each of them for a waiver when you purchase materials, for small items simply keep receipts.......you may have a "cut-off" amount like $500 and less just rely on receipts, for a $2500 HVAC unit get a waiver.

Generally, for any subs that have lien rights, you need to have the gc get properly executed partial lien releases from them as you go, then Final Releases from all subs/suppliers before making final payment to your gc.  

     I've been looking for a new supplier for wholesale flat king sheets, our existing sheets aren't quite hitting the mark. 

It also creates an estimate that I have sent out to my suppliers to get quotes for flooring/ windows ect.4.

The best way to do this is to get a spreadsheet and then start pricing materials at your local box store and other suppliers.

Update: Oceanpointe (supplier to MI) has re-invented itself as Freeportinvest.com.

I think it comes down to the contractor and the paint supplier. 

Following this logic you could profit by creating a similar contract and personally taking the form of the bank (fund supplier) and contractor (installer).

Any way you slice it, paying suppliers with credit cards will not secure you the best price because of that 2-3% charge.