Going on my wife's experiences as a courier a few years ago, the biggest proportion of clients are lawers. If there are lots of lawers in your town you should do ok. However, if there are no existing bike couriers in your area, perhaps it'd pay to find out why before throwing too much money into it (it could be simply that it hasn't occured to anyone yet).

I do admire what you're trying to do though, so good luck, it deserves to succeed.

PS. If 'nike courier' didn't yeild many results in your search engine, try 'bike messenger', which I believe is a more common term for it in North America.