Non-guest parking via adjacent BAP lot — from $10/day, Gateway shuttle
The Hilton SFO Bayfront offers non-guest parking effectively through the adjacent Burlingame Airport Parking (BAP) lot at ~$10-15/day. Direct rate at the hotel is $40/day — use BAP or SpotHero for the cheaper rate.
Shuttle is operated by Gateway Global, shared with BAP. Runs every 10-15 minutes but reliability is frequently criticized in reviews. Located on Airport Blvd in Burlingame.

Great value — from $7/day via aggregators, free 24-hour shuttle
$10/day, free shared shuttle every 30 min — no hotel stay required
Shared shuttle with Hyatt, every 15 min — cheaper via SpotHero/Groupon
Covered garage from $11/day — shared shuttle with Marriott, every 15 min