As stated in the title this fire pit cost me about $110 for the raw materials. The inner diameter is 40 in (102 cm) while the outer is 54 in (137 cm). I purchased materials from both Home Depot and Lowes and I recommend visiting both because they had different block colors and sizing if you want to create a variation of this pit.
Raw Materials: 6 bags of .5 cu ft of drainage gravel (Lowes)
42 Retaining Wall Blocks (Home Depot)
Angle Grinder with concrete-ready blade (only needed if you get blocks that do not have two level faces)
Step 1: Place 14 Blocks in Circle
You could use a string and two pencils to mark out a more perfect circle, but I found it easiest to just lay the blocks in the best circle I could. Then, use a shovel or a stick to mark the outer and inner edges of the blocks.
I would also like to note at this point that you could use any number of blocks for different size fire pits and 12 would actually be the easiest to set up because the angles work the best. I chose 14 simply because I liked that size.