I contacted number of barns around me while back to see if I can ride in the arena for an hour or two. The only barn that turned me down was in fact rescue. All others were OK, and the price was $15-25/hour (depending on place).
BTW, I did ask if I can "rent" in my emails (although in 1 or 2 the owner stated that I may not be the only one to ride, the borders can be there too).
"Life isn't about waiting for the storm to pass: it's about learning to dance in the rain..."
"When we are no longer able to change a situation - we are challenged to change ourselves."
"How people treat you is their karma; how you react is yours."