swandiver
War Child
ISFJ here
I don't think it's really necessary to pay money for the official test, spend a little while studying each function and how they correspond to the MBTI type and you'll be all the more knowledgeable for it.
The type I got from the basic test described me perfectly enough so I didn't do too much searching. Nonetheless, really useful stuff to learn (you might get into the habit of typing friends/acquaintances, though).