It is everything mentioned above, plus you have to factor in the general condition of the floor and are there any difficult areas. Same old, same old, tradefolks look at every job different. Every one is unique, plus a lot depends on their work load at the time. You don't tend to give super bargains when booked in overload. Lots of competition typically gives a lower price, they only can charge what the market will bear.
Location is a biggy, the number of folks in the business.
Yes, I would avoid general handy men like the plague, get somebody who does it everyday and is well equipped to deal with your floor.
If the floor requires extensive sanding or repair you can expect to pay more. If it is just a lite sanding and refinish then you get a better deal. It is possible to do a chemical prep with little or no sanding, usually they use a screen to buff out instead of sanding, quick and cheap. Depends on how picky you want to be. Areas that require hand work add to the job cost, especially if there is a a lot of it like a counter overhang kick space, etc. Sometimes sanding is not required, they can do a cleaning procedure and refinish immediately, might be possible if the old finish is in good repair. You didn't give any pixs as a guide.
The price of materials especially the finish effects the final price. Just remember the customer pays for everything. Also remember many tradefolks work portal to portal. They factor in things like travel time, time to do the quote, etc. Someone very local is usually going to have the better price.
As mentioned the quality of the finish product is important, plus how many coats are they using.
Just a guess, $700-800 dollars might be a good price for a room of that size, with moderate prep. What I remember from the Boston area a few years back. Price is anything the market will bear and how established the fellow is.