For an "in barn" lesson with my coach I pay $85 for 45 minutes. In a clinic it's about $175 for 45 minutes.
Another clinician I bring in is about $135 for 45 minutes.
Other people I've ridden with are up to $350 for 45 minutes.
$50 is great!
I have never paid more than 25 dollars for a lesson, and I have ridden with a couple really good trainers. I think the average for my area is around 35.