I have an attached one car garage where the floor slab seems to have sunken in one corner by about an inch and a half and varies lesser amounts in other areas. The slabs continues behind the garage into our stairwell (the house in on a hill and the main living are is one level above the garage).
We want to fix the slab in the stairwell and would prefer to make the fix in the garage as well. We have so far gotten a quote for "slabjacking" using polymer foam for around $1,500. Other options are to use a special bonding top-coat cement mix to level out the slab while also inject some of the mix into the cracks about the edges. That cement mix is not cheap ($15 for a 40lb bag) but because of the thickness needed I don't imagine it would require that many bags.
FYI, we moved into the house about a year and a half ago and haven't noticed any sinking. The house is 50+ years old so the sinking may have happened gradually.