The most efficient and therefore the cheapest to run AC unit is a split system, with a fixed unit on an outside wall and a separate unit on an inside wall. You can use it for cooling in summer and cheap heating in winter, hence doubling its utility.

I suggest you contact a couple of AC contractors and see whether your apartment is suitable. If it is then you would be advised to contact the landlord before commencing work.

You may need to get somebody to cut a ductwork in the wall. Alternatively, you might install a mini-split ductless Heat Pump.

You can also find an A/C unit that is just for sliding windows, a window unit that is vertical.

they have 2 hoses in a frame that you put in the window like a window fan, so it can exhaust the hot air and bring in fresh air

Do a search for portable AC units, they are common.

My apartment has vertical windows leading to the balcony but that's it. I want to have something that can cool my apartment but I'm not exactly sure how portable/vertical air conditioners would work. It gets cold where I live so I want something that's convenient to put away in the winter.

I guess an air conditioner needs a vent to outside but is there anything else that could work similarly maybe?

Thanks.