A go - is.............. let me think of how to say this.
Ok, you're at a bowling alley, you are with 5 friends, they all throw the ball but they do it one person at a time, they all have "a go" their go.
"Let me try, it's my go".
To charge for something $1.99 a go, means $1.99 for every time you buy it.
I'm stunned at some of the poor answers in here sometimes.