beelzerob, The $225-275 range is good, the base is worth $70, you want the base for the $275 or less. You can take a risk and let him stew a day or two, but you might regret waiting.
Start the conversation with, you really want a grizzly jointer, and that if you buy one used vs new the deal has to be exceptional to fore go a full warranty and just plain having a "new" piece of equipment.
Let him know the new G0654 6" x 46" Jointer is $425, so you are wrestling with do I pay for new, or pay $30 in gas plus $300 or $330 for a $100 dollar savings, and no warranty. Make me an offer I can't refuse. Your best deal would be $225 for both, your goal is $250 buy you would be willing to pay $275, you will have to decide if you are willing to pay $300.
Ask him what is the lowest he would go for the jointer and the base.
One other thing, is let say he says $300, and you feel this guy won't budge. Ask him if he has anything else he can throw into the deal so you feel you got a deal?
BTW I paid $225 for the G1182HW
his starting price was $270, however I told him I would bring more cash if he had something else I could buy. I bought 8 clamps for $50
which I saved about 50-65% on they were used but in excellent shape (not the best deal on the clamps but combined it was a great deal).