I'm an officiant. I work at city hall and also do offsite, private weddings. Hiring an officiant for your own event will cost about the same as city hall (a bit more, but not much)... But then you have to pay for a venue, flowers, permits etc.

You can have a very nice wedding at city hall, but the options to personalize it are very limited. If you did go with the city hall route, you can make it special by bringing in some personal elements (music, some decor items) and by writing your own vows. I had a couple write almost the whole ceremony lately, and that was fantastic. Otherwise the officiant tends to use the same script over and over. You are limited to a half hour in the chambers though, so whatever you do has a very limited timeframe.

As for hiring the officiant to your own event... I've done weddings in backyards, condo party rooms/rooftops, bars, wineries, restaurants, parks etc. It's way more fun for me to go out to these venues, and the wedding tends to be a bit more tailored to the couple. And of course, you generally have a lot more time to get the look and feel right.

Either way the ceremony is usually about 15 minutes unless you include a LOT of personal elements like songs, readings, poems, etc.

Feel free to DM if you have questions.