Looking to heat/cool a 20f x 40f building cheaply

Have a building/shed I use for hobbies and hanging out in. It has two windows on one of the long and short sides, and one window sil that the original owner put in, but then decided not to use and ran the outside wall and siding over. Tempature wise it regularly hits 95+ from mid may to mid September. It may go below 32' (0c) for 15-20 days in the winter and generally hovers around the low 40's otherwise. We might get one week of sub 20' weather, but I'm not going to be doing anything out there in that weather anyway. Summer humidity runs 80+ until August when it dries out. Winter is generally less humid, but also less dry times.
I had to rip out all of the fiberglass insulation as it had insect and rodent damage, but will re-insulate when I can afford it.
With the descriptive novel out of the way, I need a way to cool and potentially heat this area, cooling being the most important. Humidity removal is also a need, but again secondary. This will be something that is turned on before I go inside and turned off when I leave, not constantly on. A window ac unit seems like the logical choice, and possibly using a small space heater in the winter. Could also move it into the main house for an emergency if needed. With winter coming up I was wondering if there would be any clearance units on sale, or a recommended brand or one to avoid, and general advice.
For the advice of do the insulation first, money isn't the big issue, it's the time and downtime of the building, also I hate putting in fiberglass insulation, and it seems to be the best option usually.