Was that 1,500 per person or 1,500 for the boat and all the people that can fit?
For the whole boat. But if you tried to take a lot of people, they would probably want to charge you more. Also, if you want to go really far down the beach, they will charge more. I swear, those guys make A LOT of money off of taking people out there, because it's really not that far at all on a bot. For sure more than they do fishing.
You CAN walk out there, and in fact I have when I went with a bunch of school kids on a field trip. But it's HOT HOT HOT midday and like walking through a desert, I'd say it's 5 km or so. There is a stunning view on the way, before you walk down the hill to get to the beach, that's where most of the high-up pics you see of the beach are taken from.
The least I have ever paid, about 2 years ago, was 1,200. Of course there are no set prices, so try to bargain. If you are going to rent a car to make the trip out anyway, think about this: if it costs more or less 1,500 more to rent a 4x4 than a car, might as well get the 4x4 because then you can go and leave whenever you want, and also drive from one end of the beach to another.
I also recommend taking snorkeling gear (if you have it) to Bahia because you can see some things, like the big starfish and maybe sting rays, a few fish. But don't expect to see any reefs.
They recently built a nice bathroom in la Cueva, good place to change before heading out.