Hardwood floors contractors will quote you usually by the foot.
In our area, a good, experienced, preferred contractor will be between 2.75 and 3.50 a sq ft.
Sometimes price will depend on finish wanted, number of coats (usually 3 is best), and perhaps on the layout of the house or rooms. If there are alot of small, cut-up rooms, the sanding takes more time and there are more corners to scrap. This may cost more.
I would recommend getting references or a referral from someone very happy with their floor. Also helpful to ask how long the contractor has been doing refinishing, if he belongs to the National Wood Flooring Assoc., is he licensed and INSURED (!) and does he just do hardwood floors (owns his own equipment) or is he more a handyman and rents equipment.
Hope this helps.
If you haven't guessed...we are in the business. I run the office for our hardwood floor company...my Dh has been doing them 20yrs.