What should I do with my leftover bench flour? I make bread/pizza quite often, up to a few times per week. I work on a wooden surface for forming the dough and use a flour dredge to spread about 1 cup of flour per session on my surface. I would like to use more flour but don't like wasting the fairly expensive 00 flour I work with.  When I'm done making the pizza, I usually just scrape all of the leftover bench flour into the trash.

I would like to know if I can consider reusing the bench flour after it has come into contact with my dough, hands, and work surface. Would I be introducing bacteria or other unpleasant things into my flour bag if I put the flour back into it? Is there a different method I should use to keep the bench flour around for the next session?
The main problem I see is humidity - the bench flour can be lumpy, have bits of dough in it and will be partly moist. I would therefore not put it back in the main bag of flour. 

If you use it like flour, it might leave dry lumps, so it depends on your technique whether it will work or not.
But there are techniques in bread baking that use leftover dough or even dry ground and soaked bread in new loaves - that's where I'd put it. 

It can go into pre-ferments (even without yeast or starter), improving gluten development and dough texture. Unless it's absolutely dry, I recommend storing it in the freezer until your next baking day.

Apart from that: unless you are actively working the bench flour into your dough (vs. using just a bit to prevent sticking), have you considered using a "cheaper" flour?