22 acres equals 106,000 square yards. Conservative Estimate minimum $1 per cubic yard, that would make a 3 foot cut over entire 22 acres about $100,000 and your only three foot down. I know very little about construction costs in real world, but 22 acre lake going to cost major bucks on relatively flat ground. True cost is dependent on cubic yards moved x rate per yard. Takes some surveying to find how many yards need to be moved.
Experienced contributor will be along with better info. Welcome to the forum.