It depends upon the specs involved. Bids can vary by how busy they are, how hungry they are for the job, if they have or need to rent a bobcat/backhoe and truck to tear out old drive and make the grade, and if they are on the same page (usually they have their own ideas) for the specs.
Around here they get $2 to $2.50 per sqft for flat work for a 4" slab along with minor grade preparation. For a drive you need at least 5" of 3000# concrete and 6" wouldn't hurt if you park any heavy vehicles on it. So for flat work alone I can see about $1000 to 2000 depending upon how thick.
For tearing out a drive, that is hard work and dodgeman is about right with a backhoe and truck and it may take longer and more people. I just spent a couple days tearing out a concrete porch of 250 sq.ft. with 6.5 hours on the bobcat hour meter. Two of us spent a half day with a jack hammer and sledge hammer and alot of hand work cutting wire and rebar, etc and it was in a hard to reach place and then we had to brace up the roof and work around braces and trees. Tearing out concrete is hard on equipment.
Don't allow them to pour it right on the soil. Require that it be poured on compacted sand/gravel of at least 4" to 6" for a solid subgrade. Make sure the soil is very dry (wet soil will move later) and don't do a pour in the rain. Also require expansion cuts with a concrete saw in 10' squares or so with the depth of the cut at least 1/4 of the thickness of the concrete. Put expansion joints by the house and street and any sidewalks. Require remesh and rebar to be placed down. Gravel and concrete saw blades are expensive.
Write up a list of specifications and go talk to each contractor about their bid and what it includes especially if you didn't do this before and just called them to bid a new drive. They may end up adjusting their bids. Pick the one you are most comfortable with. You probably just want a brush finish so you aren't to concerned about finish work. See what equipment they have such as power screeds, compactors, metal forms, cutting torch, bobcats, trucks, etc. Owning equipment is expensive and helps the costs but then they are the ones that are in business and not a couple of college kids making extra money.(Are they a concrete contractor(specializing in concrete) or do they do general contracting?