Hmmmmmm. A taxi to Marina Del Ray would run you probably $25 each way, for $50. If you know a destination, fine, but it could be a long walk from one end to the other if you don't and are just cruising. I prefer the Santa Monica idea. If you can't stand the bus idea, Thrifty at LAX usually rents compacts (neons) for about $26, and you'd have freedom. Check the parking charge, if any, and go for a hotel without one to keep this cost low. And fill up the tank for about $2 before you return the car to avoid a ripoff.

If you've got lotsa time, Manhattan Beach, Venice, Marina Del Ray, Downtown Santa Monica (3rd Street Promenade, the Park over the Beach, and the Pier), and the Ocean Park section of SM are all interesting and close.