Class prices will vary based on several factors including overhead, competition and market. I do not think volume has anything to do with the equation as both St. Louis City and St. Louis County have issued more permits then KC and it's counties. Probably has more to do with the cost of overhead and competition. For example, since I run my classes on my property in the next county west of St. Louis I have a lower overhead then those who have to rent classroom and range space. My disadvantage is outdoor range work no matter the weather.
I think if you did a little more digging you would see that the pricing between east and west sides of the state probably would be closer to even.