Well, you've got a couple of people to contact and get input about San Clemente and Coastal Oregon. Those are also the areas I'm familiar with. I'll talk more about ideas since the others didn't.
So Cal-- SUPER STRONG appreciation. High price point entry. What's your budget? San Clemente is great area and less expensive than many areas to the north of it (Newport Beach through Malibu). San Diego is cheaper generally and Oceanside is very cheap. There's lots of direct, inexpensive flights from Denver to SNA or SAN. That would make it easier to get to from Denver, if that's where you're flying from. There's lots of competition for vacation rentals, but the market is strong and demand is high. Expect greater demand if you've got an ocean view, and even more if you can walk or bike to the beach. Ocean front has the highest demand. Summer time is usually booked out, winter rentals are more sporadic.
Coastal Oregon-- beautiful and runs less than half price from So Cal. Sometimes, if you're looking down near the California state line along the Southern Coast, the entry price is more like 25-30% of what it would cost in So Cal. Oceanfront/bayfront/lakefront/riverfront is possible. Huge panoramic views of river, bay or ocean are there to be had. Why is it cheap? Because that southern coast is hard to get to! There are no easy ways to access the very northern coast of California (The Lost Coast) or southern Oregon. It's a long drive from pretty much anywhere. We opted for Coos County due to affordability and proximity to an airport that has flights from two hubs (SFO & DEN). As a general rule of thumb- The closer to Portland you get, the pricier the real estate becomes. The more remote areas would have less of a VRBO draw off season, but Portland would be more year-round. It's easy to fly to PDX from anywhere in the world.
Florida- I would think it would be very easy to find a beach location to buy that's affordable. Much of the construction is newer and there is lots to chose from. However, I'd never buy a vacation home in a place I've never seen, and you shouldn't either. IMO, there's not much that interests me to see in Florida. If you are a boater, that would be different. I can't speak to the VRBO market, either. Usually when people are raving about how great an area is, it's saturated.
Myrtle Beach-- more activities in the area, lots of history. Some interesting looking older homes that vary in price. If you got an old duplex, you could claim one side and rent out the other, maybe throwing in a little sweat equity for a rehab. I think your families would enjoy exploring the area, if the travel time allows.
How about Texas or Louisiana? Very affordable options along the coast in both states. And they are half the distance from the East Coast from you, although I don't know much about the ease of getting flights to Louisiana. Texas obviously has huge airline hubs and lots of flights.
Don't forget that you can sell the house if it doesn't work out. So try it for a few years, then reassess.