Remove existing concrete with a skid loader; jack hammer first then bucket, truck and haul 10 miles, will costs about $3.00/s.f. + $50.00/mile.
Evaluate sub-base by a soils engineer; determine why the floor cracked. You will have to pay the engineer something.
Mitigate problem soil conditions. This could be the most expensive component and it's impossible to estimate because you don't yet know what the problem is.
R&R sub-base, provide and compact structural backfill, will cost about $200/cubic yard. If the garage is 1,000 s.f. and you have to remove 18" soil then the cost would be about $11,000. That's just one possible solution. Don't know if that will solve the problem until engineer has evaluated.
Another possible solution could be that all you have to do is recompact the existing sub-base. That would be a lot cheaper.
Since you live in Minnesota and assuming that the garage is not heated, then your problem may be subsurface moisture freeze/thaw. If that's the case, then you have to determine where the moisture is coming from and deal with that first, then recompact the sub-base.
Provide and install new 4" concrete (3,000 p.s.i., max 5" slump) with 6x6-10x10 welded wire fabric will cost about $6.00/s.f.
KC
