I don't know much but I do know it is usually a lot cheaper to adopt them from a breeder or something than a pet store.
You'll be completely fine! This is coming from someone who had THREE wild rabbits at once, while living in an apartment with a small attached backyard. You can easily feed them, since they are vegetarians and will eat grass or hay. Their pooping is very mess-free since they are compact dry pellets, but you will need train it like a dog and take it out for a walk so it won't pee and poop everywhere in the house. You will need a harness leash for this, so they won't hop off. We had house cages that we put them in when we went to sleep, since they weren't potty-trained. The cages served as a "litter pen" for them to use during the night. Then , we would empty them out in the morning. All in all, they are pets that you can treat a lot like dogs and cats (have a litter pen in the house, potty-train, take for daily walks, play with, etc.), but they are WAY more inexpensive since you don't have to buy special food (the rabbit food pellets are not necessary).
And just for credibility, here's a link for more info: https://www.rspca.org.uk/adviceandwelfare/pets/rabbits/diet
It depends on your environment I would say. For example, it's fairly warm where I live and we often let our bunny roams in a small area of our backyard and it eats grass thrown in with a few carrots. We take him inside the house at night and you can potty train your bunny so that it's easier to clean up messes. As far as I know, monthly expenses aren't a problem. If you're going to buy rabbit food, then I suggested searching up feeding amount just in case of overfeeding.
Anyone with a pet rabbit know how expensive it is to take care of one? I have an opportunity to adopt a rescued one but I'm afraid I may not be financially ready as this would be my first pet on my own!! Any other tips would be appreciated too :3