A smelly infection is bad. Cleaning and such will only do so much. Antibiotics are most likely needed and if the infection is really bad, the vet may need to do some surgical intervention. Your cat really needs to be seen by a vet. Try one of these organizations for help:
Your vet may offer financial help of some sort. Or look for a low cost vet clinic in your area. Some people start a GoFund Me page or just ask friends and family for help.