Here in Canada I pay $7 for a big bale of pine shavings. My feed lasts me a month and I'm feeding 10 Chickens and 5 Call Ducks. The feed I use is a Grower finisher feed for Chickens, Ducks, Turkeys and Geese. It's $15 a bag.
I only use straw in the winter. In summer it rots quickly due to the wet poop from Ducks..
I have stopped using straw in my run in warmer months, but in winter, it seems to help insulate them and I just keep adding more over the frozen straw/poop mix until it thaws in spring and I fork it all out of there. I do stil use it in my duck house all summer, but they do most of their pooping out in their run. I have had terrible luck with pine shavings getting quickly waterlogged and becoming a stinking mass. Straw is easier for me to keep aerated and drained.
My six ducks go through a bag of feed in about a month. They do not free range. I supplement their feed with weeds pulled from my yard which they love and any past-it's-prime produce from my garden. They go crazy for tomatoes and also like Swiss chard a lot. I give them vegetable scraps from my kitchen. They eat every insect that comes into their run. I have a smelly fly trap on the ouside of their run and they eat any flies that fly into the run and the traps get the rest. I usually trap and dispose of two quarts of dead flies a week in the summer.
Pest control is another cost of keeping ducks. I go through a few bags of Sweet PDZ stall refresher per year at about $10/bag. I sprinkle it on their straw to minimize moisture and odor. More moisture equals more odor, so think about that when building your duck house and enclosures. Drainage is important and will affect the cost of keeping your ducks. I also go through a couple of packages of mosquito dunks per year, putting them in the area where most of my ducks' water drains to avoid having it become a mosquito breeding area. Spray pesticides and birds aren't a good combination, but the dunks aren't harmful to them.
For flies, I use the reusable quart jar type fly traps that you put some water into and add a packet of fly attractant. They smell bad as the attractant activates, so I have one one the outside of the run and one on our back fence. They were about $10 apiece and a package of ten attractant packs is about $10. You can get disposable traps, too, for about the same price per unit. But I trap two quarts of flies per week, which would be $20 per week for the privilege of just dropping them into a trash bag and putting them out with the trash. That's out of my price range. So I don the plastic gloves every week, fill the run trap with water all the way to the top and put a brick on the popup lid to keep it sealed so all the flies and maggots inside will drown, then move the back fence trap up to the run to catch all the flies that were coming to the now closed trap. Once everything has drowned, I put on new gloves again and empty the drowned stuff into a garbage bag , rinse it out into the bag and tie the bag closed completely (because it stinks and I don't want the bait to get on anything and attract flies). I put it out with our trash. Usually during those few hours, the other fly trap has filled up and I close and drown it, while rebaiting and hanging the empty trap on the run again. A few hours later, I don new gloves again and empty the other trap into another bag and put it out with the trash, rebait it and put it on the back fence.
I know this sounds completely gross and it is. But dealing with flies is part of keeping ducks. I welcome the spiders that set up in our run. They just can't keep up with the flies. I tried putting both traps away from the run, but I still had a lot of flies come to the run, despite that I hose it out two or three times a day. So I decided it was better to trap them where they were coming anyway. My neighbors are happy because they have many fewer flies due to my traps. Predatory wasps don't do well in our climate and are also expensive, given that they will not naturalize here and have to be replenished every month of the warmer weather. Rodent control is also important, so sealing your duck house against mice and rats and protecting their food may involve some cost, though it's usually not an ongoing outlay. Consider your own circumstances and your own sensibilities and add in the cost of pest control to your calculations.
