We are fortunate enough to live on Cape Cod, so we'd choose here (has a top 10 rated beach - Coast Guard in Eastham).
I would guess it's fairly expensive, especially if you're looking at rentals. However, you could probably get a decent deal next season, since a lot of rentals went empty last year. I can't really comment on cost of other expenses, since it's our everyday and that's tough to compare.
I can say that we go on vacation to NH and we feel it's cheaper to go there, so I guess that means it's expensive here.
We live 20 minutes from a very nice beach area-Tybee Island near Savannah. The beach is nice and not extremely crowded. You can see dolphins from the beach, my DH gets on his boogie board (with a life jacket and flippers) and gets right out there with them! We usually stay away during the really hot months, but spring and fall are great!
We are in Delaware. We go to Rehoboth Beach for a week or a day (staying at the family 'beach house') whenever we get a chance.
rehoboth beach,DE
We've stayed 3 Fall Breaks at Majestic Sun, part of the Seascape Resort.