I'd recommend going far south, Avon, Frisco, Buxton, Hatteras and Ocracoak. The prices there are better. We always stay in Frisco. There you are never more then two houses from the beach and always have ocean views. We use Midgettrealty.com They are fantastic.
Bring some staples. Go to Avon to the Foodlion and stock up rather then using the local store. Grill and cook at home almost every night. Go to the seafood market one night and get special treats to grill. Go to Ocracoke to the Pelican from 3-5 I believe, for ten cent shrimp that are great. Have fires on the beach and roast marshmallows.
It's very informal. By staying that far south there is little to spend your money on. There is one mini-golf/go-cart place. You can also spend an afternoon biking around Ocracoke and doing a bit of shopping. Go to the Graveyard of the Atlantic Museum, which is small but cool and donation only.
Just spend your days on the beach. Bring kites and surf poles. Spend your evenings grilling, nights on your deck sipping drinks or on beach bonfires. It's our favorite place to go. I'll be taking my kids for a week in March during spring break. Dirt cheap then.
Oh go to the light house. It's also really cool to go at night when the light is on. My kids have gone with bunches of friends and played freedom under the lighthouse.