How much do you charge for private lessons?

Long time lurker; first time poster.

I'm an instructor and recently I've been getting more and more requests to do one-on-one private lessons from my students. I'm struggling with how much to charge. My studio let's us choose our rates but there is the studio rental fee to consider which is $40/hr. I want to have a reasonable enough rate that I can build a solid clientele base but I still get paid adequately. I'm thinking $90. $40 for studio rental and $50 for the lesson. Does this seem reasonable? How much do y'all charge for privates?