I agree with Cheryl.
The value of a Disney resort (and I'm assuming you're going deluxe if you're seeing that much disparity between on property prices and off property) is really in the "extras"
- Free transportation from the airport to Disney
- Free transportation within Disney World
- Free parking at all parks (if you have a car)
- Resort package delivery
- Resort charging privileges
- Access to the Extra Magic Hours benefit (much more time in the parks)
- Access to purchasing the Disney Dining Plan
and, I'm sure, others that I've forgotten.
Many, many people enjoy off-site accomodations, but I feel that staying on property is best for my family and our style of vacation.
Eileen