There are a few things you can do than buy top shelf feed for your ducks and chickens. First off I assume you pen your flocks up, as I rarely feed my free-ranging chickens as they prefer to find their own food & will only eat out of the feed bowls if they happen to wander by them. I feed my penned up hens Hubbard's Layer Feed and supplement it with table scraps. I pay $12 a 50 lb bag, but I also buy from another breeder, who buys in bulk. Now I do put out 2 bowls of feed for them in the morning and I mix in water with it, making a porridge out of it. Otherwise the ducks will carry dry feed to their water bowl to moisten it, and waste a lot of food. Plus dry feed tends to block their nasal passages which they blow out at the water bowl. But after they fill their craw, then tend to want to find a mud puddle to root around for worms, bugs, grubs, and roots for the rest of their nutrition.
Second, if you have the means, you can find a local farmer who makes his own poultry feed, and contact them for prices, which is always cheaper than what you will find in the feed stores. Where I am located, the Amish make a Chicken mash, for $20 per hundred pounds, and it is exactly the same stuff they feed their own flocks. The Ducks will eat it, but don't like it as much as they like the processed crumble, which is ok, as they will just forage more, (I think it has to do with Texture, more than taste).
Third, if you have the means, you can find a local mill that will grind you what you want. In the fall, you can bring in a ton of shell corn and a ton of alfalfa, oats, wheat, or whatever you want in your mix, and they will usually add the minerals & vitamins, then bag it up in either 50 to 100 lb sacks for you. If you contact Purina they are usually helpful in finding a custom mill that is near you, even if they are a competitor. Most custom mills belong to the Amish again.
Fourth, I look for sales especially at roadside fruit & veggie stands, and I buy my flocks whatever is in season, but isn't fit for human consumption, such as cracked watermelons, pumpkins, apples etc...They will bring you bushels of bruised fruits & veggies just to get rid of it. Also if you tell them that you will be feeding it to your flocks, tend to cut you a deal if you buy in bulk, 4 or 5 melons instead of just one. Get Old Jack o'latern pumpkins after Halloween, (Pumpkins & seeds are great for Deworming your flocks as well).
Fifth, Find restaurants with Salad Bars. They throw away a ton of fresh veggies every night and day old bread too, just ask them about retrieving it. Do not feed your poultry flocks any meat.
Sixth, you can make your own Chicken Treats of Black fly larvae, if you can stand the smell of rotting flesh, (Of which I can, by my neighbors don't).
Hope this helps!