The main difference between getting a free kitten to getting one from a shelter is that the one from the shelter is already vetted and known to be healthy. The free kitten may not be healthy and will need all its shots (in most cases). You may want to try to find someone that needs to rehome a young cat they have that already has shots and stuff but isn't asking a huge fee. Adult cats are great too. But if you really want a kitten and can't afford the adoption fee at a shelter then just keep looking. You will find the right one sooner or later.