So, as someone who hates the heat, and is an idiot, I have a 3-floor a-frame (steep) design log cabin in the south. It's a lovely house but it has some issues. The biggest one is the AC. It has an HVAC system that I believe was originally put in for the 1st (half underground) and 2nd floors. The 3rd floor was finished later on and added a master bed and bathroom and a loft office space.

The main issue is the the loft, which is about 400 sq ft and sits over an open high-ceiling living/great room. That space is around 1400sq ft.

The basement is cold in winter (doesn't seem to heat properly), the 2nd or middle floor is always just about right (i.e. the AC can keep it in the low 70s even in July/August) but the loft space is like hell. The space also has 4 computers in it, adding to the temp. When it's 72 in the great room, it's easily 83-88 in the loft, where I work and spend most of my time.

There is a high window level with the loft, at about 20' from the great room floor. I placed a window AC unit in it but of course most of its cold air falls down to the great room, making it cooler than desired down there. The window is about 3' from the loft rail.

There is only one HVAC system air vent on the whole 3rd floor, in the master BR. It gets limited cool air flow. The bedroom is north facing and shaded and with the limited flow stays livable outside July and August.

The AC system seemingly can't cope and I can't afford what I believe is 10-12k to install a new system with zoned controls and all new vents.

I'm wondering what options I do have:

a. There's a closed/sealed skylight in the roof, above the loft space. Given hot air rises, would I benefit much by trying to get some kind of venting skylight to replace it?
b. Are there other ways to vent the hot air out of the 3rd floor that won't cost a kidney?
c. Any ideas on how best to create some kind of DIY duct from the high window unit over to the loft? I'm not good at such so it would need to be somewhat simple. The duct would have to connect to the casement style window unit and then traverse across 3' to the loft rail and then into the office space somehow. Ideas?
d. Other suggestions/ideas, apart from moving to Montana?