Try buying some wheat, barley, or cracked corn. These are cheaper and are good. Dont give to much cracked corn as it is not very nutritious. Also feeding them treats every so often will make them eat less feed. I chop up peas, cucumbers, and lettuce and put it in water then they love eating it. Hope this helps.
Natural Best cheap feeds I've tried are dandilion greens, chick weed, alfalfa/clover/"sheeps rock", lichens, moss, or Get a kiddie pool, trough, bucket, ect, and grow algea, duckweed, or water hythinth (may need freeze protection by bringing some in in containers in winter). Put mosquito fish in and they'll eat extra mosquito and provide enjoyment and animal proteins as snails will. (And rosy/chub minnows). worms grown in compost soil and duck manure (redworms and earthworms supposed best), but mealworms can be left to grow in dry compost of soil poop and anything natural (they are actually scavenger beetles loving warm compost growing much better than bran raised) you will need to put some fencing around whole or part of so they cannot devour too much too fast till gets established, maybe leaving gaps in so they can get heads in to feed from part but not get at and make mess of whole. don't feed grain especially corn ect as takes away from nutrition of pellets/crumble/mash made feeds and then they take more nutrition to offset junkfood and balance and having complete feed (supposedly) is wasted then your throwing money away. the fat in corn only good for meat ducks and winter feed. i do feed cheap scratch grains, but just one or other as seem need.
another more gross way to feed is to get a bucket with little holes in bottom and hang out with some sort of soil and some off meat that attracts flies and larve from will fall through holes and amuse feeding ducks chooks ect (I've never tried yet).
In nice weather I take mine for walks and they eat slugs and worms and other invertebrates, a big protein boost - no money spent.
In winter, I can provide them some green stuff by sprouting wheat seeds that I buy in bulk. That costs a lot less than buying lettuce.
Also, in warmer weather, I can grow lettuce for them. And they like weeds like chickweed, dandelion, violets they like okay, the seeds from lady's thumb (a smartweed).
Some restaurants and organic grocery stores will give you bags of vegetable trimmings. Just check through it first to make sure no one dropped in a bit of trash (my nightmare would be pop top rings - metal poisoning!)