help!!

hi everyone,
i sort of adopted a 10+ year old, not spayed, cat from my neighbor in April. she's pretty neurotic, really picky about her litter box, initally scared of most people. since april she's been throwing up on and off, and i feel like i've tried everything. i feed her purina cat food's special hair ball control formula (is this a bad brand?).i bought this hair ball controll gel that you're supposed to stick on her paw so she'll look it off. She HATES it though, and i could never get it on her. instead i put it inside a little ball of tuna fish (is that a bad idea?). yesterday morning i woke up to the sound of her gagging gagging gagging. only white foamy stuff came up every once in a while. usually she throws of food and/or hairballs. i'm really worried about her and this whole barfing situation just doesnt seem normal to be going on this constantly! i also got a cat brush to groom her with, though it didnt seem to be getting much hair.
any and all advice would be MUCH appreciated,
thanks,
naomidoo

Please take your kitty to the vet if you haven't already. She is in need of a complete check-up. She could have worms or something worse. It is wonderful that you have adopted this stray, but a vet is the way to go here.

okay, more questions, though i don't know if anybody will beable to provide answers for some of them.
i took this cat home on my own. that is, my parents (i'm 17) aren't going to contribute anything to anything that has to do with her (ie a trip to the vet). i'm pretty low on money, how much do vet check ups usually cost? are there such thing as free animal clinics? this cat is an indoor cat, and she's only been outside of the apartment building once, and that was when she was a kitten. i tried to get my neighbor the owner to take her to the vet before i took her, but he said it was unnecessary and would just freak her our for nothing.
unrelated (or is it..?) for the past few weeks she's been doing this weird thing of getting really really mad at her tail and grabbing it and hissing it. is that just some odd game to her? anyone else have a cat that does/ did that?
thanks a lot.

I can't give you an exact answer, but I can try to give you a general idea of veterinary costs. At the clinic I use it costs between $16.00 - $20.00 for an office visit, which includes a basic physical examination of the cat. There are additional charges added on to the cost of the office visit if any tests need to be run or medication needs to be prescribed.

Since you're only 17, you may want to try to find a vet who will allow you to set up a payment plan if it becomes necessary.