please forgive me if you answered or addressed this question and i missed it;
i'm assuming if your cat was kept overnight, your vet was able to see him trying to cough up the hairball and is sure that it's a hairball problem and not something else?
ONLY reason i ask is that i've got two cats who cough from time to time and never had a hair ball come up (no, correction, ONE time one of them did have a hairball, but only once)
anyway it turns out that they have asthma
they cough,basically, as if they have a hairball or might be about to throw up- and many many ppl think that their cats have hair balls when they actually have asthma
just something you might want to double check.
asthma is pretty easy to treat once it's been diagnosed
hope your kitty continues to do well and that your financial situation improves! i know what that's like