REtail wise, yes, hardwood can generally be cheaper. But, I was at BMO a few weeks ago and they had boxes and boxes of slates at what I remember to be 10x10 (?) and $5 (?) a sp ft. It's Builders Materials Outlet on Hwy 55, just north of the 149 junction, by the ULine warehouse. You can also google search them. Anyone can go in and buy, but it's a crapshoot, they may or may not have it or enough, but it can make a dent in the final price, even if you have to buy some at retail or through your contractor. Personally, I like mixed media and would go for the slate. Good luck!