Ok I live at a boarding stable, and keep my horse here for free because I do all the work during the week and get the weekend off.
We charge 250$ (CAD) per month for feed 2x/day, paddocks picked 5 days/week, waters filled/scrubbed every 3-4 days, blankets on/off.
Full access to an outdoor arena, tack room and some tack, as long as you ask
I don't know how much hay costs for everyone else, but our barn gets a super good deal on hay. It costs us only 120$ to feed each horse per month, and it usually costs about 180$.
The barn owner also buys dewormer in bulk and charges 10$ per tube for name brand dewormer and hold horses for farrier, will administer shots etc. Also, she is good friends with the vet (and the vet is nearby) so there is no charge for a vet to visit, only for the vet services.
This is in BC, Canada.
I don't think there is a cheaper facility in the Okanagan here... I searched hard.