Metro Bus to Amador Causeway?

I was wondering the same thing last week and made several inquiries at the Metro Bus offices. The information window at Albrook told me that there was an older non-Metro bus operating between Amador and Cinco de Mayo.
I subsequently walked all the way from the Figali Convention Center to the end of the Amador Causeway, Isla Flamenco where the Cruise ship passengers go through customs on their day visits to the city. I saw no city buses, although there were city bus stops on the route, and many private buses as well as that red double-decker "hopon-hopoff" bus.
I'm guessing that after the traffic nightmare caused by all the metro construction in the city has subsided, some sort of city bus service may resume.
Until then, the choice is taxi or the red double-decker.

As far as I know the buses are still running from Cinco de Mayo to the Causeway, but it's not the normal buses. They use the coaster style ones and only go between those two places. The stop at Cinco de Mayo is just around the corner from Ave Central on a side street, when they come back they let you off under the overpass.

And taxis are only 2,50 from downtown, right?

Probably at least $5, maybe a little more. This is one area where you usually end up paying more than you're supposed to, especially coming back as theres not always that many taxis out there.