My opinion, it depends on how well the trip went. When I have been on trips in the past, you pay $100 a person for example, if it was just a good trip you may tip $10- $20 dollars. If it was the time of your life, with a trophy fish to go along with it, probably $30 or so.
I struggled with how much my first time, I felt like I was already paying him $100, but in the time spent with the guide you will build a connection and most likely have an awesome and unforgettable time. But it is all about what you feel comfortable doing.
Just remember that any tip will be much appreciated.