Hotels in San Francisco aren't necessarily cheap. You'll want to make sure you're in a good neighborhood too–be aware of the Tenderloin neighborhood, which you should absolutely avoid.
This is where most of the wedding evening / night festivities will be taking place. Historic, Classic, Fancy. We will be staying here the night of the wedding.
Hyatt Regency Embarcadero
Also very reasonably priced and a nice hotel. It sits right on Market street, near the Ferry Building. Bonus: you can ride the cable car up California street and hop off right in front of the Fairmont.
5 blocks downhill from the farimont and in the heart of the very touristy Union Square district. Also very close to MUNI & BART trains.
You honestly can't beat this price for a centrally located SF hotel. It's a no frills type joint, but it's 3 blocks (downhill) from the Fairmont. Just remember, don't go west into the Tenderloin.
City Hall is the orange pin and the Fairmont is the green pin. Walking is possible, but the hills in SF can be treacherous.
The area in red is the part of San Francisco known as The Tenderloin. It's not a great part of town. A lot of the drug activity happens here. Lots of people are living on the streets here. If you want to see this kind of thing, you'll be ok during the day (just keep moving). Otherwise, it is highly advised to stay out of this area.
Yes, City Hall is near The Tenderloin, which also sits between the ceremony and the festivities. You'll be ok standing outside City Hall and in the park across the street. Call an Uber.
Airbnb can be a fun way to experience life in the city. There are many options from studio apartments to entier victorian style homes.
What to Bring
San Francisco gets cold! The arctic breeze off the ocean / bay is no joke. Bring warmer clothes than you think.
San Francisco is a walking city, so bring your walking shoes and prepare for the hills.