Hey Boss. Welcome. Not sure about the gravel or springs except that the lower the springs are the more chance of the water pressure from the pond stopping or even reversing them. My guy told me springs are great at water level but other than that you don't want to hit them.As far as cost I'm also in Illinois (south central) I had about a one acre pond built for around 8000 that was also taking out some trees before they started. It was 100 an hour and he had two pieces of machinery running the whole time. So it was 200 an hour. Not sure if that helps but I'm sure you'll get some better advice than what i can give.
