They charge by weight. Some boats pay as much as $240,000 to get through the canal. The cheapest fare ever was a guy by the name of Halliburton, who swam across in the 30's and only paid 37 cents.
Notice in the last three photos how they lower and raise the water to let the boats through the locks. So fascinating. It takes about 8 to 10 hours to make the 50 mile trip. There are several sets of locks. This one I photographed is called Miraflores, and it's the largest set.
In the last two weeks, they have had so much rain, that for the first time EVER, the canal was closed for 17 hours!