The reality is that riding the horse likely costs them nothing. These kids are all members of the FFA. So, there’s a good bet that they already owned the horses, already had to feed them, and need to regularly ride the horses anyway.
So riding the horses to school is essentially free. I spent most of my life in a town where a good percentage of the population uses horses as their sole means of transportation (e.g., there are places for people to tie their horse at the local grocery stores, etc.)
What these kids are doing makes a lot of sense. Free leisurely transportation to school that is also fun. However, it really isn’t possible in most of San Diego where people don’t have barns.