I used 17 80# bags of quick crete, some re-bar, to make the base. It's ~7.5' in diameter.
I used/recycled castle-wall stone that was local and unused/abandoned for years. I bought a bag of mortar and some cap stones to make this:
It's "great dane" approved
I used ~80 of the blocks, 17 of the capstones, a large bag of mortar, and 17 80# bags of quick-crete. Cost was around $75 as I had most of the stone for free. Would have been ~$125 to buy it all (estimate). It's large enough to burn a pallet easily, so I anticipate lighting a bunch of things on fire
Not sure if I need to use fire-brick in the bottom of it. Plan on "breaking it in" this coming weekend. Anyone here is invited down, wife/kids out of town for the entire week....
I built mine pretty much like yours only just bare dirt base two rows high and no mortar or rebar. That was 4 or 5 years ago and its just fine. I think I scooped it out once and dumped the ashes in the swamp.