If the medication is strictly for cough from collapsing trachea, or kennel cough than any cough suppressant should be effective. Prescription cough suppressants are usually human preparations that contain codeine or hydrocodone. Many of these are available in combination with an anti-histamine in a cough syrup and some are in tablet form. Your vet can give you a prescription of one that is appropriate for your dog's condition and the medication can be filled at a human pharmacy. There are generic preparations that are not costly.
Butorphanol is an analgesic (pain medication) that also acts as a cough suppressant. If your dog is taking this medication because he has an issue with pain as well as a cough than it would be best to keep him on it. It may be available as a generic, and therefore less expensive, at an online pharmacy, or may be less expensive at a Walmart pharmacy.
What is causing the cough? Thats the question that needs to be addressed. I'm assuming you are working with your vet about it?
Do you mean butorphonal (Torbugesic, Torbutrol)? That med is for pain relief, at least that's how we use it at work.