If Paris associates with Eiffel Tower, and Rome with Colosseum, Cotonou should with Zem Zem. Yeah I know you're going to ask so here is a map...its the biggest city in Benin, a sliver of land nation in West Africa, between Nigeria and Togo
With a population of about 800k people there are over 150,000 registered moto taxis, also known as Zemidjan or Zem meaning "take me quickly" in local Fon language. Zem taxis are everywhere, recognizable by their yellow jackets, the drivers cruise around in search of customers or are can be found around almost every corner. It's not an easy work; there is no insurance, no social benefits, exposure to pollution, and of course accidents (~400 fatal per year). But, with 30-40 customers a day many can make 150,000-200,000CFA (~$300) per month, which is about 5 times the minimum wage of 30,000CFA.
The city lives because of these taxis. They are the cheapest, fastest, easiest and most common way to travel around Cotonou, although not the safest. So make sure you tell the driver to go slow or gently ("aller doucement" in French)...and wear a helmet if the driver has an extra one.
The cost depends on how far you are going but usually 500-1000, cheaper for locals. As an example I paid 1,200 for a half hour ride to Calavi (boat dock to Ganvie). If anyone starts talking thousands for a trip in the city, just offer him 500, max 1000 or walk away to the next one, you'll find the China effect..the further you go the more price drops.