I before got interferon injection for my hepatitis b 3 to 4 years ago but its too expensive is there any other alternative that is cheaper?

Yes: Interferon for hepatitis b is given for a finite duration. Either it works to cause the virus to go into remission or it doesn't. If continued treatment is required, there are many antiviral agents that are effective. While these are much cheaper than interferon, there still very expensive and treatment may be lifelong. There are several manufacture assistance program available.