if it's hairballs you can buy catlax or laxatone, but you really should take your kitty to the vet as it could be a sign of something more serious.
I noticed a lot of people have reservations about taking their kitties to the vet when their strapped for cash but honestly a check up visit to the vet is only about $20...
The other posters have given excellent advice which I hope you follow -- caring for a cat is like caring for any other family member, and we need to set aside funds for their health care just as we would for ourselves, children, elders, or whomever! Good luck, and I hope your cat gets a checkup SOON, along with the proper medicine or OTC remedy.
My cat, Holly Golightly, coughs at times and she was diagnosed with asthma. I agree with the other posters that a vet visit is important to rule out more serious ailments. Vet visits are costly but important for obvious reasons. Thank heavens for credit cards and Ebay (for selling my junk!).