I refinished my living room floor six months ago so I'll give you my experience. First, know the actual condition of your floor. If its too old or too damaged no amount of refinishing will help. You should also know what you want done because there's more to it that just getting a floor sander. For example, Home Depot rents out floor sanders however, the actual sanding paper is sold separately and comes in different grades of which I don't remember anymore. Knowing what you want to do to your floor will determine the type of sandpaper to apply to the sander. If you just want to get rid of the surface layer to see the natural grain a light grade of sandpaper will do. If you have serious dings in the floor, a heavier grade is needed. The size of the room will determing how many sheets of sanding paper you will need. Also, think about whether or not you will need a hand sander for tight corners. Luckily I had a square shaped sander and no tight corners.
If you want to keep a natural look but with a shiny floor you should cover with polyurethane. There's two types: water based and oil based. From what I was told, water is good and does not stain but doesn't last as long as you'd like. The oil based lasts much longer and will give a stain to a light floor the color of honey. Of course if you wanted a darker stain you would have to do that first before putting down the polyurethane. I push the polyurethane because it will seal everything in and protect your finish. I have a very small living room and the process took a day to complete.
All in all, the size of room and condition of the floor will determine how much this will cost you. I got everything from Home Depot and I think I paid about $130 for everything. The Sander rental is on a 4 hour basis so if you can guestimate how long it will take you that will help you with assessing cost.
Hope this helps.