The cost depends heavily on the pond site and to a lesser extent where in the country it is being built. Many contractors look at the cubic yards to moved and the distance it must be moved and also on how the dam needs to be built. A 5 acre pond could just require a short dam across a gully all the way up to a fully excavated pond with a long core trench where clay must be brought in to act as core material and a full clay liner is needed. Having a good understanding of how to build a pond and knowing the soil profile down to below the future pond bottom is key to estimating the cost. And even then, costs can rise if unexpected veins of permeable material are found during the construction, or you hit high volume springs that flood the pond. On my second pond, the contractor hit a spring that flowed like an open fire hydrant and added 3' of water to the bottom of the pond in a few hours. Fortunately, the pond was near complete so it worked out fine. On my last 2 ponds, I hit water-filled sand veins that required a bottom drain be installed to continue work. I had the drop to use gravity, otherwise it would have required a pump. You can get an idea on cost based on cubic yardage, but you need a pond builder on site to estimate the cost on that sight, and not just a dirt mover. When I had my first pond built at just over 1 acre, it cost me twice what the same contractor estimated for a friend to build a 5 acre pond because of the topography and sight conditions, and the friend lived more than twice as far from that contractor than I did. I think these variables are why no one else has weighed in. I wish things were more simple and wish you the best of luck finding a place that works well for you!