Thanks for all the replies, advice and suggestions guy!
Few things:
1. Bus is 12 row sized
2. Bus is stationary (for the time being)
3. Bus is mostly stored under shade (just about all but dog nose)
4. Solution is temporary so looking for easiest route/cheapest route but, if keeping cool enough means spending a little money then I'm for it
5. I'm, at some point, Getting rid of the windows for RV style ones but that's a whole other situation
6. I intend to install a mini split A/C or 2 for my permanent A/C solution
I was looking at portable ac units before starting this thread but since a lot of the reviews of the ones I've looked at and the fact that it seems like installation required some type of hose, I didn't know. Like a few people suggested, I might go with a window unit.
One concern I have based on a few replies suggesting to take the inside ceiling skins down, old insulation out, put new insulation up and then new ceiling up is I was planning on taking the inside skins and insulation out as my next conversion step but wasn't quite ready to put new insulation or ceiling in yet. On top of that, if I do take the insulation out with the Houston summer heat creeping up seems like a bad idea..? On top of that, I wanna raise the roof on my build but am still researching the easiest way to go about that (aka, hesitating because I'm scared and have no experience nor knowledge

)
At the end of the day, I'm leaning towards a window unit. Anyone ever install one in a skool bus with the stock windows? Hope its as easy as I imagine.