I understand your issue with an AC unit. My shop building is 30' x 60' x10' ceiling, insulated tight, no windows. My biggest problem was getting an HVAC company to install a system to my specs and not what their computer system told them to put in. They wanted about a 3ton system. That would not dehumidify at all. I did not want cold air I wanted dehumidified air. Finally got a guy to put in a 1ton unit and a multi speed fan. I run it at a slow fan speed. I live in NW ILL lots of humidity, shop stays at about 35 to 40 on worst day. AC set to 70 or 68 and on hot humid days it runs about 50% of the time as it cannot keep the temp that low, but sucks the water out of the air. I have what is called a high efficiency system, not sure about the temps you mention. I do not let the fan run all the time because of the fact that then the remaining condensation just goes back into the shop defeating the purpose of the whole design. I have no idea how much water it pulls as it dumps into a rock bed outside the shop.
BTW had same problem getting the correct size heating system, the computer wanted 200K BTU system, my calculations called for 60K system, I put in a 80K system, again at my insistence and it works just fine, nice and toasty even at at -20 outside. My slab has insulation under it and up the sides, as would have been spec'd for an in slab heating system.
Bob