Remember, you not only have to remove the popcorn texture, but also redo the ceiling in some other texture.
Price will depend on several factors:
1) how much the contractor you choose hates removing popcorn or textured ceilings - some charge $1 or so/SF extra just because they hate it. There are even some who bid total drywall replacement cheaper than removing the popcorn, so you have to first find contractors who are happy to do that work, or your prices will be out of the realistic range
2) if the popcorn predates about 1990, then it could likely have asbestos in it, which doubles or triples the price, and in many cases uncapsulating it with a spray coating and then removing the drywall entirely is actually cheaper than all the protective measures necessary if it is scraped off.
3) whether the popcorn is primarily gypsum and vermiculite (comes off REAL easy) or was the plaster of paris variety, which takes a fair amount of soaking to soften it enough to scrape off
4) what type of finish you are replacing it with - if a textured ceiling, slapcoat, knockdown finish or paneling, not real problem. If you want to go with a perfectly smooth ceiling (generally a bad idea as any variations in the drywall on a ceiling surface really shows up dramatically), then it will demand a lot of care in preparing the scraped surface, and a complete surface drywall compound skim coat to smooth out the scrapes and gouges from the removal process.
5) what underlying conditions are - if there is a lot of furniture to move around (should go to adjacent rooms) or cover and work around, high-quality rug or hardwood floor to super-protect or such, will drive cost up.
I have seen costs run from as low as $0.60/SF to $1.25/SF (for removal only). Generally, remove and recoat with a surface texture of some kind (anything but smooth) and paint will run you about $2.50-3.50/SF.
Now the bad news - if asbestos containing, can run from $5-10/SF. Many homeowners in that situation go the other legal route - have it encapsulated with an asbestos-rated sealant by an asbestos contractor, then paint it and leave it for the next homeowner to decide what to do about it. Some contractors encapsulate it and then put a 1/4" thick drywall layer over it - this usually looks like a disaster unless it has a VERY rough textured finish on it, because putting drywall sheet over a rough surface like popcorn invariably means a wavy surface commonly looks like a gently rolling ocean surface.