There are tons of parking lots and garages in Santa Monica that you can choose from, but if you are staying for just a short time, the best place to park is at any of the city owned lots. You get the first 90 minutes free.
The parking lots along the beach offer reasonable flat parking rates, but they fill up fast. A better option would be to park around 3rd street, which is within easy walking distance to the beach and pier.
Santa Monica has a lot of metered parking in the area. Meters typically charge $1-$2 per hour with a 2 hour time limit. This 2 hour time limit is a strict parking maximum for Santa Monica streets. You CANNOT park at the same spot for more than 2 hours, even if your meter hasn't expired. If you are parked for more than 2 hours without moving your car, you will get a ticket!
We highly recommend leaving extra time for parking so plan ahead for a stress-free day.