Thanks, I bet that will add a lovely odour to the chook run.... LOL It would be cost effective if you make fish dinners and can use your own scraps, but if you have to buy them, it probably will still cost what the baits cost. They are convenient in that you can just keep them in the shed...
These
http://www.bunnings.com.au/trap-the-buzz-fly-and-wasp-trap-2-pack_p3010324
Or this is the jumbo size
http://www.bunnings.com.au/envirosafe-fly-trap-with-refill_p4475914
Notice the yellow lids. Flies are attracted to the colour. Also, you are supposed to hang them down near ground...