Hey there! Congrats.
Your best bet is duckling feed, starter from 0-3 weeks and grower from 3-14 weeks. 18% is a good protein percentage.
Do not feed chicken starter or grower. It will harm your waterfowl due to different niacin requirements.
Then afterwards, the cheapest feed is an 16-22% maintenece feed (all flock or waterfowl, duck or goose). Provide oystershell on the side for calcium. Why maintenence vs layer? Well, layer feed is designed for laying birds. Geese are seasonal layers, so feeding lay feed to non-laying birds can be harmful. If you have a gander, laying feed can harm him. Maintence feed is cheaper and safe for ALL birds, and if you provide oystershell on the side, instead of layer feed, they can eat the calcium and lay at their leisure.
Geese do not roost.
In winter when they can not graze or find their own food you can feed table scraps like fruits and vegetables. Avoid bad, spoiled food, or avocados, potato peels, and chocolate.
How many are you getting? What kind of living arrangement will they have? Will they be on a pond? Will they be sexed?