Typical is 3-5% of the job cost.
Well for one example… I had my wife call and get a price on Versa-Lok blocks (They told her $7.35 per block)… Then I called and asked them what the contractors price was on Versa-Lok Blocks (She had forgot to say that we are contractors, lol) And they were $5.15 per block. I had to show them my License, though.