How the hell do I get my room un-hot

A couple of these may be worth a try: acinfinity.com/register-booster-fans/

I haven't used these particular products but have had good experiences with other AC Infinity stuff.

Since when do mini splits cost 10-15k?

a 12,000btu unit would easily cool that. You can get a unit like that to DIY install for like $800-1500. Installed probably under 3k if you cant do the power yourself.

Seems like the way to go. They aren't silent but can be very quiet. So at the back of the room should be fine.

You need to exhaust the hot air!

And a new mini split for that size room, should not be more that 3k to 5k at most, installed.

I had to replace my mini-split about 3 years ago (its 18K btu or 1.5 ton). yes, they can leak after time, and when they are already 10 years old, you can't always get parts so you get to replace it...     anyway it was under $4K installed (Texas).  

I don't have any real "exhaust" and no returns since it is the mini-split, it mostly recirculates (except when the door is open).  I can also freeze you out if that's what you want, and my room is 475 sq ft with 10 foot walls and a 15 ft vaulted ceiling -- in other words a bit more space to cool than yours. And I'm in Texas, but I do have thick walls (2x6 and brick exterior) and the room is pretty well sealed airtight.   You might not even need a 12K btu/1ton to cool that room?

No

I just don’t think I’m willing to put that kind of money into it. Plus, the only place to put the actual unit - as my studio is at the front of the house on the second story - would be in the front of the house. And that ain’t happening.

How far away is the nearest return vent? If there is one in the next room over I’d investigate popping into that one and running a line to your room. Probably the cheapest option. Air can’t get in your room to cool it because there is no air leaving. Fix that issue and you might be golden.

Oh - it’s in the next room. This room is off of a kind of open area playroom…the return is in that room.

Man, when I had all my analog stuff running and a few artists sweating through takes in the studio, it would be 80F+ in the room in the dead of winter and I'd even turn the AC on in january.

Since going mostly ITB, I rarely have any issues with temps in the room.

But either way, YES, a return is NECESSARY. Not just a vent out of the room, but an actual return that can suck the hot air out.

We required fans and heat sinks for the tubes at Motown.

Ok I'm pretty sure I see what's going on and its a typical 'home studio' problem... there's a lotta stuff going on in a fairly small space, and with the dormers & A frame, despite the deep footprint that's a fairly small space and the stock AC just isn't keeping up. 

aka - not enough horsepower! 

Looks like the vents, at least one is like a 6x9..? Rectangular about midway down the left side wall by the lamps? And there's probably another directly across from it? And those are open? System is on and you feel a breeze of cold air..?  They aren't closed or blocked or something kinda dumb? 

All that gear generates a lotta heat and yeah, recording studios are probably one of the few places on the planet that run freeze box AC in the middle of January in Alaska. Big honkin large format consoles, even some outboard racks might have AC vented in... Have to otherwise the SSL computer tower will cook itself to death. 

Main thing would be to increase airflow around the room itself. Get a fan... tower fan? Stick it in the corner and let it run. I really LOVE these honeywell turbo fans... can often find 'em in stores, depot, wally for under $20.

www.honeywellstore.com/store/products/honeywell-turboforce-air-circulator-fan-ht-900.htm

My old shop had some poor circulation as well & these fans, on low speed are quiet enough that you can hide 'em in corners... behind racks, those chairs or whatever and you don't really hear them. Not over cranked guitar amps or rock & roll drums anyway and they'll help keep the air from getting stale. 

Popping a dedicated return into the room may not actually be the best move... or depending on how the house is framed, even really possible without $$$$ 

If the return, sucking air out isn't installed right it can be really noisy. Even done right it could be jet engine loud... that's the $$ part. The intake at my new shop, in the soundlock hallway is easily the loudest part of the entire AC system... the registers in either room make almost zero noise. The heat pump & duct work is on the backside of whats going to be the tracking room and it barely makes a rumble... easily ignored for all but the very most critical quiet stuff 

Truth is for 'general domestic use' that A frame studio space is probably fine with the return in the other, main room. The "problem" is as studio rats we'll stuff that room with all kinds of space heaters (tube gear) maybe a couple 3 other people and close the door for 6-12 hours a day, and so it gets really freakin' hot!! 

Essentially best move, if you absolutely have to work with the door closed all the time? Gotta turn that room into its own "zone" - and the easiest, cheapest method is what Eric said and toss a window AC unit in to chill the room out between takes & ear breaks. That and get fans to keep air moving / exhaust out the open door... whenever its open! 

Best move would be have someone carve a hole in the wall and install a split ductless. You'll probably have to pull down some of those panels to find a slot in the walls... re-arrange the layout... but it'd be worth it... 

Or - hey - why not move outta there and annex the bigger room outside..? Even some of it? Probably somewhere else in the house you can stuff an amp closet...

Maybe what 'ya really need is a bigger workshop! 

John,
I had a small room set up a few years ago, approx. the size of yours, and I put one of these AC units in the window.

www.lowes.com/pd/Midea-Midea-8-000-BTU-U-Shaped-Air-Conditioner/5000281553

It was surprisingly quiet, because the compressor and noise making stuff stays on the outside, other side of the window.
I see you have a window at the far end of the room, this would be a good spot as it's away from where you record vocals & guitars.

I set it up in the far corner window, and was able to record Acoustic guitar, vocals, and drums while it was running.
But if I needed to do something in total since, I just shut it off, and started it again when done.
Never even noticed it, while editing or mixing.

It was cheap and worked great for my purpose.
Something to consider

Actually it's still in storage in NY, otherwise I'd give it to ya!

Don't need it here in the new joint in Hartsville.