Most people who have pets are only interested in having something cute and fluffy hanging around the house. They're not interested in adapting their condo to accommodate the animal, in laying out money for its care, or of inconveniencing themselves so that the animal has what it needs. But if you're a pet owner, you're legally and morally obligated to not just own the animal but to care for it as well. Before you buy or adopt a pet, make sure you know what's involved with its care.
Cats and dogs are the most popular pets, but owning them is a significant expense. They will need regular needles to protect them against everything from rabies to fleas and they will need to be neutered or spayed to help cut down the population of unwanted animals. The bill at your animal hospital may be a thousand dollars a year or more if your pet develops an ailment, especially a chronic one like diabetes, or gets injured on their insulated concrete job. You should be prepared for that expense.
You may be thinking to yourself that you don't want to spend the money to get proper medical care for your pet. Isn't giving it a warm place to sleep in your home enough? No, it is not. If you are having these thoughts it would be best if you didn't get an animal. Buy a plant or a statue of a dog. Don't get an animal if you're not planning to look after it. Not giving your animal its vaccines and checkups will make it very difficult for you to take it anywhere, especially by plane, as they require proof of immunization.
As for other types of pets, even small ones like guinea pigs, hamsters, and fish require care. You cannot buy a fish and expect that your only efforts on its behalf will be to sprinkle fish food into its tank. It needs a tank that is properly sized for it (1 inch of fish per gallon of water). It also needs an aerator to put the required amount of oxygen in the water, and its tank will need regular cleaning and water changes so that its fecal matter doesn't build up and choke it.
It's not possible for us to outline all of the vet bills and ownership expenses that come with getting each type of pet. All we can say is that we hope you do your research before you decide to take animals into your homes. Remember: animals may not be able to speak, but they do feel, and mistreating or failing to look after one is wrong. You should be prepared to accept your pet into your family, not just your house, and treat it as you would a child or relative when it gets sick.