If you are handy, resourceful, and creative, you might be able to keep the expense down. It also depends on your location (cost of supplies and site specific concerns).
Had I known what I found out at the beginning of winter, I would not have built the duck house as I did. We ended up keeping the ducks in the walkout basement at night, and now that's where their pen is. It works out very well. Certainly don't have to worry about raccoons breaking in at night - though we did have a baby possum sneak in one afternoon when I had the door open and I wandered off for a while. I am much better about closing the basement door now.
Don't cut corners with keeping them safe from predators. If they are not in the house at night (not a nightmare, really, if you have a little space in a utility room or similar), then their house must be sturdy, with no openings larger than half an inch, no latches that something could jiggle loose, no boards something could pry apart. No dirt floor something could dig under and into. I think you get the idea.
Organic layer pellets here in Southern New England cost me $27 per fifty pound bag (Blue Seal). Mazuri's more expensive. A bale of shavings is $6, pelleted sawdust is $7 per 30 pound bag. Six months' worth of poultry vitamins (very handy) are maybe $10.
While my tendency for younger people (any age, really) wanting ducks is to point out the responsibility side of it (I feel you are making a lifelong commitment, and ducks kept safe and healthy can live for ten years or more), they are a joy, they are therapeutic, they teach us lessons we might otherwise not learn for a long long time. And they absolutely depend upon us. They need us to protect and provide for them.
Okay, I'll hop off the soap box.
