There's absolutely nothing wrong with saying "between X and Y" in my opinion. You just always make sure X is what you actually want, and Y is at least 30% higher. Give them the opportunity to grind you down, it'll make them happy; give you the ability to say "look, I've already let you take X% off what this should cost" which will come in invaluable later, because it's an instant ego-booster for the other guy. Always let the other guy think he's won, simple rule.