check craigslist, a lot of places sell plastic barrels that might work well. The smaller 20, 25 or 30 gallon variety might be the perfect size. You could easily sawzall the top off or part of the top off and leave the bottom half of the lid so the eggs don't roll out.
If you look at this link you can see in the picture in front of the 55 gallon barrels a group of smaller ones. Those are the perfect size. I see others on CL in the Indy area sell the smaller barrels too. By us the smaller barrels go for $5 or less each if they are not rated as food grade. For the pond, you don't need food grade.
CL ad for plastic barrels Check this option too:
$10 each
