I agree with UDog---if the floors are in good condition you can do it yourself. Try the buffer as UDog suggested; if necessary rent an orbital sander from Home Depot for $50 a day, plus sandpaper sheets. Apply poly with a thin pad applicator with long handle. It will be really hard to screw it up to the point that it shows. I laid, sanded and varnished 900 square feet of red oak 3/4 T&G in my current home with no previous experience.
I'm going to be doing the same thing in a couple of weeks in a house I just bought for my daughter. It has nine-inch oak blocks in four rooms; no damage, just age (50+ years)and some wear.
Remember, perfect is nice, but it ain't mandatory. A great part of the floor will be covered up by rugs or furniture.