Is it a male or female?
I have quite a bit of experience with regards to taking in feral cats. All 4 of my current kitties were feral,2 of them took many, many years to establish trust with.
I'm not going to lie, if you bring it in, it won't be cheap. You'll need to get it seen by a vet, tested, vaccinated and treated. You will also need to get it fixed, otherwise it's going to want to mark it's territory inside and sneak outside, often not coming back for days.
As far as non financial risk to yourself, it doesn't seem like you're dealing with a cat with rabies and have already established a connection with the kitty, your biggest risk would probably be it getting angry at you for not letting it out. Getting it fixed will help with that. Good luck!