Unless this is like a temporary apartment or something, paint and the like are the type of thing that shouldn’t be done as cheaply as possible. Don’t spend 4 figures on paint but get a decent/mid tier brand that you think you will like looking at every day. Test on a small area first, test a few different types even. Take your time and do it in a day with low humidity so it actually dries. Do more than one coat if you have to. I don’t think a whole room for under $100 is even possible unless you’re stealing from construction sites.