As an engineer, I cannot resist solving this problem:
First, however, double check your units on the 700 sq in for the Stubbs hickory. This unit does not make sense as it is an area not a volume.
If this is a plank which is 1" thick then it can be turned into a volume and compared to the rest. If it is random chunks, then they need to get a new packaging consultant to mark their bags correctly.
The quick conversion of cubic inches to cubic feet: take the cubic inches and divide by 1728.
The conversion of cubic feet to inches: take the cubic ft and multiply by 1728.
Flyingbassman is right that the weight to volume conversion will change based on the density of the wood you're comparing...and the underlying price per pound will also change with the wood type (apple wood is significantly more expensive than mesquite per pound).
However, what you're looking for is a comparative basis not a lab analysis. I found a couple of bags of hickory online that had both the weight and volume printed on the bag (Western Hickory Chunks $8.95, 10lb, 1/3 cubic ft). Assuming all the brands you listed were all chunks of roughly the same size, then this can be used to compare the lot: 30 lb of hickory chunks = 1 cubic ft of hickory chunks
Doitbest- 9$ for 10lbs (570 in3 / 0.33 ft3) = $0.90/lb
hd/Lowes- 7$ for 5lbs of weber (285 in3 / 0.165 ft3) = $1.40/lb
16$ for 18 lbs of char broil brand (1026 in3 / 0.594 ft3) = $0.89/lb
8$ for 700 sq inches of stubbs hickory (assuming this is really 700 in3) = $0.59/lb
Menard's "western" brand chunks
8$ for .32 cubic feet (553 in3 / 10.7 lb) = $0.75/lb
5.50$ for 1/3 cubic feet (570 in3 / 10 lb) = $0.55/lb
8$ for 550 cubic inches (0.32 ft3 / 10.7 lb) = $0.75/lb