DIYbanter - Where to buy Unfinished Solid Hardwood flooring?

Newbie question: We would like to repair the 45 year old hardwood
floors in our Silicon Valley Bay Area home and add some new oak
flooring to our newly built extension. Our original flooring is made
of 5/16 thick solid oak strips.
We are looking for a source of Red Oak Solid Wood Unfinished strips of
2 sizes:
1. 5/16 inch thick strips - width 2 or 2-1/4 - for older parts of home
2. 3/4 inch thick strips - width 2 or 2-1/4 - for newly built
extension bedrooms

The idea is to replace all warped strips in the older parts of the
home with unfinished 5/16 inch thich strips and lay down 3/4 inch
thick unfinished strips in our newly built extension rooms, before
sanding and refinishing the old floor and the new one to one uniform
color.

5/16 thick unfinished flooring is hard to find. HomeDepot does not
carry 5/16 thick strips.
We located 2 lumber mills in the bay area that will sell 5/16 strips :
Southern Lumber @ $4.50/sq ft! And Minton's lumber @ $.87/linear foot!
The prices are way over the top as we found an online source of
prefinished Bruce Hardwood (natural reflections) for $3.1 / sq ft.
1. Why is unfinished wood more expensive than prefinished wood?
2. Do any of you pros on this board know where we can buy Unfinished
Red Oak Solid Wood flooring for reasonable prices? We prefer Select
grade, if at all there is a choice.
My husband swears that there should be reasonably priced unfinished
red oak flooring somewhere out there.
Please help, we have spent so many frustrating weekends visiting all
the Bay Area lumber mills in vain. We are willing to drive down a
couple of hundred miles if we can locate a good source. Thanks in
advance for your help.