Marine units and depth sounders

Our depth sounder is going, according to Bernie, "tango uniform".  It reads great most of the time, and that's the problem, since a depth sounder that tells you the depth when you are aground is technically accurate, but not very helpful.
We learned yesterday that fixing the depth sounder is going to be about one "marine unit", more or less.  We're hoping for less.
Since our boat is aground in 4 feet of water, that's about $250 per foot.
The list is getting longer...