Depends. New install of hardwood is typically abou $5-$6 a square foot..... Supply, install, sand and finish. More if there's old flooring to come out. Regional price differences will impact this somewhat, as will different species and grades of wood.
Installing hardwood isn't difficult, but it's hard on your back if you're not used to doing it.
What tools do you have? A compressor-driven flooring stapler makes the work a lot easier, and they can be rented for not too much. You'll save about 1/2 this way. But I'd recommend getting a pro to do the sanding, it's real easy to gouge the flooring if you're not careful. Staining and finishing you can do, there are a lot of products out there. My favorite is shellac. Yes, shellac. Nobody uses it any more, but it's fast, it's easy, and traffic wear can be repaired and feathered in easily, unlike polyurethanes. It looks better than urethanes, too, IMHO.
If you or your buddy has some carpentry tools, I'd suggest you look into doing it. There are some basic rules for getting the layout to look good, and procedures for speeding up the work, if you're thinking about it I can give you more info.