We plopped down our $20 and were good to go. Here's the two-adult surrey we rented, with travelswithkuma in the command seat giving directions. Regrettably, by city ordinance, surreys aren't allowed on the Promenade, so we were limited to city streets between US-101 and the Prom and between 12th St and Avenue U. That's still several miles of streets, so we gave it a go.
Halfway through the trip we traded off and let me drive for a while. I really wished for rear-view mirrors. We ended up going up a few streets that are relatively steep, and it was hard work pumping the thing through the turnaround circle at the End of the Trail monument, particularly because you can't stand up to pump on the pedals as you might do on a bicycle.
After about an hour and twenty minutes, we gave up and turned in the surrey, then went and got one last elephant ear pastry on the grounds that all of that pedaling must have been good for something.
I'm glad we did that rental. If we ever do decide to buy one of these things, the basic model (about $1500) won't do. We'll need one of the seven-speed models with accessories (like rear-view mirrors and running lights), and we'll need one custom made so it's a bit longer and taller to fit our taller-than-average frames.