The weather's been nicer the last couple days, so hopefully we'll get to move forward on this tank soon. I decided to go to the landscaping place yesterday and get the rocks for the tank. They had some really nice dark gray ones called "black pineapple." Not sure who comes up with these names.
210 pounds worth total. 170 pounds of the big ones and each bag has 20 pounds of smaller ones. Two different sizes. It was less than $60 for all of it, so definitely cheap compared to what seiryu or similar would have been.
Here's one of the big ones with a USB drive for size reference because, why not. I don't own a BIC which seems to be the standard for size reference around the interwebs.
The hardware store a couple miles from us carries the black blasting media, so that will be the next purchase.