There are many people still under the impression that it's cheaper to spend a week at the beach than to go on a Disney vacation. I maintain that depending on how and when you vacation, the expense can be very similar and even less, when all the costs are tabulated.
Granted, if you're driving to the beaches in Delaware or Jersey, you're not going to spent the same as I will for an airline ticket. But the costs of lodging, eating out and entertainment at the shore might just put you right up there!
Yes, you can go to the shore and rent a house/condo and cook your meals all week and save a lot. But let's say you don't cook and you eat all your meals out.

Here's my comparison based on staying 7 nights:

Disney Value Resort: $82/night
Beach condo: $200/night (Myrtle Beach)
Disney Meals for 4: $0 (Aug. free dining)
Beach Meals for 4: $1,100
airline tickets: $800
Beach trip Gas: $320
Disney park tickets: $1,200
Myrtle Beach Dixie Stamped: $200
Disney transportation to/from airport: $0
Myrtle Beach Water park: $200
Myrtle Beach Miniature Golf: $60
Myrtle Beach Aquarium: $120
Myrtle Beach Car trip check-up: $75
Myrtle Beach Total: $3,225
Disney trip total: $2,574

These numbers are based on actual expenses from our Myrtle Beach 2005 trip and our Disney 2004 trip. Free dining has been offered in Disney in certain weeks in August for the past 4 years, so if you can go during those last few weeks of August, you can have all your meals free!
Even if you go to Disney and there's not free dining, we've calculated our food expenses for 2 adults and 2 teens to be about $900 for the week. That pushes the cost higher than the beach trip, but not by much!