First, my regular rate doesn’t go down for Personal Training clients no matter how many sessions they purchase. I do shorter sessions for less, but that fee is at a higher per minute rate than a full hour. My doctor doesn’t do that and what I do for clients is far more life altering than getting over a cold. A good trainer puts in a lot of time to create programs and keep up their knowledge. My doctor tells me that I personally put in about 3 times as much effort in my education than he does.
Second, my small group rate is never less than my one on one rate. It is far more work for me to implement a program for additional people. Each person in a group splits the rate between them. That rate is less for each than the one on one rate, but significantly ups the amount charged. So, in your example of $75, my fee would be $120 for the session or $60 each for 2 people. Small groups do get a reduction in fees for a long term commitment. That reflects that after the initial few weeks of trainnig, I don’t need as much time to prepare. And the group dynamic begins to also improve the overall effort needed to deliver the sessions.