All the times I have priced it, Disney is cheaper.
Now, here is why:
Flights from MSP to MCO are cheaper than flights from MSP to almost anywhere else. I can still get to MCO for about $200/rt. Pricing out flying to a "beach destination" (we looked at Outer Banks, Hilton Head, and Tybee Island), is about double that.
WDW - we don't need a car. So, saves $250 or so right there.
We don't do the parks most trips these days. So, that right there is a good $2000 we don't spend. At a beach, we would be content to do "the beach" every other day or so, but we would be running around doing mini-golf, fishing, boat rides, and the like, too. Which, would eat up $$$.
A lot of the stuff we do at WDW is super cheap or free. We spend a lot of time at the pool, playing ping pong (Pop), watching the animals (AKL), playing tetherball, watching the blacksmiths, watching the horses, laying on the beach (Ft Wilderness), or perusing the Boardwalk.
We bring breakfast stuff, snack for lunch, and a sit down dinner. I hate cooking on vacation, so we would probably do the same for a beach vacation.
So, for us, WDW is always the cheapest option.
But, I REALLLLLLY want to do a beach vacation on of these years. Maybe when my boys are a little older and enjoy "down time" a bit more.
ETA - we did a "beach vacation", Wisconsin-style a few weeks ago. Cabin on a lake. We dropped the same amount of money we would have had we gone to WDW the same week.