This is a tough one to guess because it depends on how much sanding will be needed. If you have to completely remove the finish, lots of sand paper (which is costly). The rental of a sander isn't much per day, but they get you on the paper.
If the floor is a bit warped, that gets you to because you have to get down in the valleys. If it's nice and flat, it's fairly easy.
There are two ways, the drum sander and the 'buffer' sander. The drum is usually used if you need to do some leveling. If there are uneven areas and you actually want to sand wood down. Makes a lot of dust.
The 'buffer' type is essentially a floor buffer with a special pad that allows you to use sandpaper instead. This is used for scuffing the finish and also removing it entirely, provided the floor is pretty flat.
The tool and sanding technique that I use depends on the job, so Florcraft is right, it's a tough call.
If the sanding is done well, the staining and finish aren't hard. If you have stains, you have to bleach the wood, that's time consuming. You mop the floor with bleach (don't buy that 'special wood bleach', it's a scam), rinse, mop again, rinse, until you get the stain removed (and you have to bleach the WHOLE floor so that things match up nicely).
I charge $4/square foot. 1000 square foot that is in nominal shape will take me 6-8 days with 3 coats of poly. (I don't use the water based stuff as I don't like the finish). You also have to stay off of it (furniture anyway) for another couple of days. Light traffic is OK the next day. That price doesn't include me moving any furniture
Most of that is labor, materials isn't all that much.