The Just Cavern Tile Set includes 21 Cavern Tiles
This is  ~.31 Cents a square inch. 
 
Cavern Tiles (21 Pieces): 208 Sq Inches of playable 
 
9 - 2x2 Tiles 1/2" Deep 
4 - 4x4 Tiles 1/2" Deep
2 - 6x6 Tiles 1/2" Deep
1 4x4 Raised Tile 1 & 1/4" Deep
5 - 2x2 Rased Tiles 1  & 1/4" Deep