There are no free dogs. Even if you get one for nothing, it will need shots, spaying or neutering, heartworm tests and preventatives, leashes, toys, a crate, a bed, food. All this adds up to QUITE a bit of money - MUCH more than if you pay a 200$ adoption fee to a rescue and get a dog that is already spayed, has shots, been heartworm tested, etc.
Dogs are expensive. What if you get a free dog and it needs surgery or expensive treatments? Are your parents going to pay for it? This is a 10 - 15 year committment.