You've got $840 worth of stuff listed....stuff that in 10 years will probably be needing replacement. A 4" concrete pad that size (make it 9 feet wide & set the blocks on it, ends up 8' inside) would be less than 4 yards of concrete, about $300. Add in rebar and you're up around $500. 324 cement blocks brings it to $824. Have rebar stick up from the slab, put the blocks down over and mortar in place. It would be a bunch of labor, but now you can drive on it and in ten yrs it will simply be ten years old. Yaaaa, it would probably run a bit more than $824, rebar's not cheap, but with the right amount I think a block wall would work and it would be cheaper than stack-um blocks.
How much coal are you planning on? Why not make it 10 feet wide and be able to have a truck dump into it?
Lot's to think about!
If you don't want a concrete pad, I'd make a solid gravel pad and use thick felt over the gravel. You can drive on it and it'll last for years. Around here paper mills throw it out now & then.