Some suggestions for a very uneven concrete floor
We've poured over floors like this many times to "level" them out. We use a 3/8 stone 3500 psi concrete mix delivered in a concrete truck. 1 yard of concrete will cover 220 sq. ft. at 1.5 inches thick. We vacuum and wash the existing concrete to clean it, then use a primer called Weld Crete. I would recommend pouring 1.5 inches thick over the higher spots, I don't like pouring thinner than that, which means your overall coverage might be around 160 sf per yd (2" thick average over entire floor).
Concrete costs about 100.00 dollars per yard, add some fibermesh 7.00 dollars per yard and most concrete companies have a minimum charge of 4 yards for a total cost of 428.00 dollars plus tax for 640 sq. ft. of coverage.
I would hire a concrete floor contractor to place and finish the concrete, estimate 1.00 dollar per sq. ft. labor.
This should be much less than using a self leveling bag mix, we also use Mapai & Ardex products, they are expensive unless you're leveling a floor that's only out 1/2 inch or less.