Dunster is correct on the sales tax issue--while you may not be charged SALES tax because you live in a state different from where you purchased the machine, you have a legal obligation to self-report any out-of-state purchases on your state income tax return and pay your state's USE tax. The USE tax is usually the same rate as the SALES tax, and is set up for these exact situations. Of course if you happen to live in a state without sales taxes this would not apply, but just because your state does not have an INCOME tax does not exempt you from the uSE tax. (I am a CPA).
As for discounts, I always try to negotiate for a little better price on big ticket items. Plus if you offer to pay cash or check they will often take off 5 percent which they would have paid in credit card exchange fees. Never hurts to ask!! Good luck!