If you are willing to do the work the right way, you can build a quality cool room for less than half the price of a typical stand alone unit (commercial walk-in coolers). I would not bother to do it half-way.
After considerable reading and research, and a ton of work this past winter, here are my thoughts.
You MUST use rigid foam insulation, at least 4 inches in depth. Standard fiberglass simply won't cut it if you want temperatures that will make a difference.
All seams and corners must be spray foamed. You want the room as air tight as possible.
Aside from using the Cool Bot, you can not cool below 65 degrees with a window unit, no matter how many or how large a unit you use. They are designed to "stop cooling" below this temperature, and will freeze-up otherwise. The Cool Bot device "tricks" your window unit into cooling to lower temperatures, while keeping it from freezing up. However, you will still need a large btu unit to cool effectively. I'd day 18,000 btu's minimum, and the more the better.
You will need a way to bring in fresh air, on a controlled and timed interval (use a "cycle timer" that you can get at electric supply stores). In my room (15 X 12) a single bathroom vent fan has been working well. It is set to run for about 20 seconds every 3 minutes or so.
You will have to clean the room daily to the floor where there is urine. A tied calf makes it easy to control the areas that need cleaned most thoroughly. I also gently spray the vents on the window unit to remove dust each day.
I have found the the wood bedding pellets are the most absorbent and odor controling. I spray the bedding with a fine mist each morning to reduce dust.
You still need a fan or fans on the animals. A good fan at 50 degrees, combined with daily rinsing, brushing, and hair care, WILL make a big difference with your calf hair coats.