On the surface it does sound as if the 2.5 hour drive nets you a better deal but I guess you would need to factor in the free lessons learning the machine that the dealer provides. But a road trip sounds great to me to get a better deal.
BTW, if I was to consider buying an open box slightly used sewing machine from a dealer, you can bet I would negotiate that they drop the price or I wouldn't buy it. How can you sell a machine as brand new when it is sitting open to the public and has been "used", no matter how slightly.