US honeymoon ideas for two 21-year-olds

I have some friends (21 yrs old) gettjng married in late May, looking for a chill, affordable honeymoon spot in the U.S. where they can swim in the ocean, eat good food (they’re mostly vegetarian and don’t drink), and just relax for a few days.

They’re hoping for something besides Florida, but Hawaii might be a little out of budget. Open to either coasts or even islands that are easy to get to. They’re also not sure if they’ll be able to rent a car, so bonus points for somewhere that’s walkable or easy to get around without one.

Basically just want somewhere warm, beachy, and fun without breaking the bank. Any underrated beach towns or coastal spots you’d recommend for a simple, low-stress honeymoon?

TIA