"Why is unfinished wood more expensive than prefinished wood?"

In general it is not. Yes, if you compare it to the low end products
the big box stores sell. If you know the sources, unfinished products
can be 1/3 that of prefinished products but it will depend on where
you are located and the shipping distances from mills.

Pricing information of hardwood floors in general.......

http://www.hardwoodinstaller.com/har...ller/price.htm