I try to be as competitive as possible. While I don't buy in the quantities that SPI does, I think my prices are reasonable (and I don't mark up my shipping like they do either to compensate and look good on price searches).
As some of the others in this business will tell you, there's more than just price. If you want to speak to someone on how to lay out a room, what treatments are requires, how to balance things, etc. - try that at SPI.
Call Ethan, Joel, Glenn, or myself and you'll get way more in value for the advice you get than what you'll save by just buying from a warehouse.