Help: I don't understand the humor of this English joke. Ask for advice. Thank you.

A man walks into a bar and sits down. The bartender says, "It's been pouring me wine for 12 months."

So the bartender's pot was full of people he had photographed for 12 months, and they came back quickly, one after another. The bartender said, "Boy, you drink these drinks so fast."

These people say, "well, you will drink quickly. If you have it, so will I."

The bartender says, "What do you have?"

The young man said, "Seventy-five cents.