Both health resorts in Tucson, Miraval and Canyon Ranch, have historically offered large discounts in summer. That's because summer is HOT and most of their paying guests typically don't like being there when it is that hot.
But the service and accommodation level remains the same as the rest of the year, so if you can manage the heat, then go for it. A good hint for saving some money on these meal and activity inclusive resorts is that if your flight arrives after lunch or later, spend the first night at an airport hotel and then transfer to the resort just before lunch the next day.