You are in the right place. The most economical way to get a larger pond is finding the right land that does not require hollowing out a 2.5 acre hole, but just creating a dam with some excavation from the water-side and land clearing.

Typically a lay of land like that will have watershed, but of course many factors go into filling a pond that size. Worst-case is requiring a well. Best case is a nice high-flow spring above your water line. Bad case is too much watershed.