When we had the house inspected our inspector said it was
from water coming through

What was from water coming through? Mold?

I would like to grind off a few inches and poor it again

Instead of grinding you can pour self-leveling compound which is pretty
easy if you know how to mix a bag of powder with the specified amount
of water. But if your basement is big that can get quite expensive at
$28 per bag, which only covers 1/8" over 50 sq. ft., or 1" over 6.25
sq. ft. I think it is mostly portland cement in the bag.

Maybe try a local concrete dealer for pricing or hire someone to do it.