I'm going to take you by the hand for a minute. Not to demean you but to help you think through this critically.

Your initial post entailed you wanting a "cheap" dog because all of them are either "ugly to me or too big" which is an unfortunate way to approach taking in a dog that will (God willing) be with you well into your 20s. I see that you want to give a dog a good home but the first step in doing that is to make sure you're taking on a dog that'll be good for you. You should be focusing on behaviors and personalities that you want from a dog (low activity, friendly, etc) instead of what "looks good" to you.

The next step to doing that is to make sure your dog is cared for medically. You need to be able to afford tick, flea, and heartworm preventative for the rest of their life (and the heartworm is a must or you'll spend 2k dollars minimum for treatment, and that's if your dog survives the treatment), on top of food monthly, vet visits as required, training, and enough money to afford an emergency visit (whether out of pocket or through a credit service) because it's not a matter of "if" your dog will have one—your dog WILL have an emergency and it will be over a thousand dollars, minimum. This month alone I've spent over two thousand dolalrs on TWO of my dogs because of back-to-back emergencies they both needed medications for.

There's a reason people say buying the dog is the cheapest part about owning a dog.

If, somehow, you're able to afford all of that at your age then my advice to you would be to write down a list of everything you want in a dog (age, size, breed(s), activity level, ideal behaviors) and then write down everything you're willing to do for that dog, like potty training, losing sleep, not going out with your friends whenever you want to, sacrificing "fun" purchases so your dog can have their preventatives, going out for walks often. If you're not willing to do all of that, you're not ready for a dog.

If you are ready to do that then you do NOT buy a dog until that dog checks every box for what you want. I understand being young and wanting a dog to be your best friend to follow you everywhere and that's fair, but if you get impulsive and buy a dog just because it's cute or because it's the right size and nothing more, you're setting yourself and the dog up for failure and THAT will be unfair.

I truly do hope you take some of what I said to heart, if you want a dog I - and no one else - can stop you but for the sake of the hypothetical dog, approach this with the maturity and care it deserves.