Tussionex is expensive because it's seriously potent stuff. You've basically got yourself a narcotic analgesic there, so do be careful.
I assume you're shaking yourself apart coughing and unable to sleep, but you'd probably be better off with a liquid anti-histamine and some glycerin to soothe your throat. Chocolate contains a natural antitussive(theobromine). Which is addictive in other ways
When I say better off I simply mean from a financial and not-getting-addicted point of view - I do appreciate that this will work, and work very well short term.