The major cost of bring a drug to market is not the manufacturing cost, it is the testing required to sell it. This is why except for a few very old drugs all generics (out of patent medicines) were once patented drugs. The whole purpose of the patent is to allow the pharma company to charge enough initially to make a profit before they are faced with competition. Without a patent you just can't bring a new drug to market.

In regards rhinos I was responding to the claim that if the rhino horn had real medicinal value it would be farmed. It could be possible (very unlikely) that rhino horn does have real medicinal value, but there is no way of ever showing this without a patent on rhino horn. Without a patent you can't farm rhinos for medicinal purposes because you can't ever show rhino horn has medicinal value (i.e. No pharma company will invest the money required to show this without a patent).

You can't use the fact that rhinos are not farmed to prove that rhino horn has no medicinal value when there are other possible reasons that rhinos are not farmed for medicinal purposes.