yes, I have to agree, after your initial set up and bird purchase, your first breeding year should generally pay back all your cost, from then on all you have to do is cover the feed and basic up keep, which in a per bird scheme of things, no isnt much, you many have 1/2 a bag of feed per bird to grow it up so, $10 tops on most migratory duck species, now geese and swans are another story, they are bottomless pits and you feed many barely be covered on most species time you raise them.
Say you have $15-$20 per pair in expense to raise one for a few months til fall when you sell them, now think of those $200 hottentots you just bought, yes they made a profit off it. Now most just turn that money around and put it back into the birds one way or another. More birds, new pens, incubators, etc, you'll never get rich doing this, but you can definately pay for your addiction with them.