The barns in Missouri are very competitive with their prices (meaning, every barn charges pretty much the same exact price).
The particular barn I ride at (with a lesson horse OR with your own horse) is:
-Evaluation (Half an hour "orientation") costs $50.
*Every rider must complete the evaluation as it helps properly place you in the program.
-Private lessons (half an hour each) costs $50.
-Monthly package of private lessons (4 lessons per month) costs $180 ($45/lesson).
-Group lessons (which consist of 3-6 riders) and is one hour long costs $40.
-Monthly group lesson package (4 lessons total) is $140 ($35/lesson).
-Monthly group lesson package (6 lessons total) is $195 ($32/lesson).
-Monthly group lesson package (8 lessons total) is $240 ($30/lesson).
Some other facilities offer "Semi-Private" lessons which range from $40-45 for a 45 minute ride. I'm sure our facility would do that but they just don't have it listed on the price sheet.
I'm not entirely sure why prices are set at what they are...I'm sure the upkeep of the horses has a large role with it (especially if you're using the facilities horses), but I partially think it has to do with showing as well.
*Example: I live near a large horse showing community....HUGE for Hunter/Jumpers and Dressage. Put it this way, I live about 15 minutes from a National Equestrian Center--so I'm sure the lesson fees are expensive but are, of course, going to be to worth while. Most people aren't getting lessons just for pleasure riding (not saying some aren't) but are instead learning to ride well and, hopefully, place well in shows. Whereas if you consider the fees where I'm located at to facilities just a couple hours away...you can find a place that'll train you for pleasure riding for a mere $10 per lesson (45-an hour long lesson). So depending on your location, it could have a HUGE factor in the cost.
^Again, that's simply pricing for my location. :3 Good luck with your search!