I bought a 110 gallon plastic water trough for $78 at TSC; figured that it could be a swimming pool later on down the road. Good enough for eight runners to eight weeks, but just barely!LOL. Is that for a brooder? If so, you can buy yourself some time and get away with starting them in a large plastic tote.
Six ducks to ten weeks is acceptable too.
Coops take time, trust me!