FIFO Inventory Formula Challenge

Twifoo 

Robert, I was going to apologise for using your challenges to explore the developing product that is Excel and learning new techniques rather than addressing the terms of the challenge head on.  It appears that I may not be alone in this!

I did even consider using recursion to keep a running total of stock value transaction by transaction but came to the conclusion that it would be too heavy in terms of its computation and would represent overkill.  I also wondered whether there is opportunity for a greater level of nested Lambda functions to expose the overarching logic to a greater extent but getting my brain to shift gears is not coming easily!  I had a look at some theory but the function representing recursion 

λ(λx.x x) (λx.x x)

does not come easily to me.