There are a ton of variables specific to your region, project specifics, labor costs, permit requirements, etc. Factors that will greatly affect the price include access to the crawlspace, headroom, methods of getting concrete down there, etc. For this reason most of us discourage the practice of giving "estimates" or even ballpark pricing on a DIY internet site. In most cases it is a shot in the dark and does you very little good.
Your best bet is to seek out a few bids from licensed insured contractors in your area. Getting a bid doesn't obligate you to use them in any way, just don't sign anything.
Something to consider before seeking bids is whether you just want to cap the ground with a vapor barrier and concrete to clean the crawlspace up, or if you want a neatly finished flat level slab down there.