speaking of cement, have you tried looking at a small cement mixing tray? The are about 6in. - 8in. deep, and about 16in. wide by 24in. long. They are even smaller if you cut off the rounded lip around the edge.
Just throw a plexiglass section over 1/4 of the pond where the land is, and build the land on top of that if you need more land.
My vivarium has a Dish-Pan basin with the rim cut off, and rocks forming the new rim. The rocks overhang by quite a bit, to provide shelter for the fish and my tiger salamander when he is in the water. The Dish-Pan basin is a rectangular shape, with rounded corners, about 3in. deep. Only cost me about $2.00... and I think the small cement mixing basins only cost about $5.00...
Still doesn't sound good, try an "Under the bed" container, or a cheap dorm-room trash can... all about $2 - $7, and cut them down to size with a razor.
Decorate them with Flexible Fish-Tank caulking and a layer of sand or stone for a real natural look. (No painting, that will poison the creatures)