Month over Month Price Change (with last available price)

[pawelj795]

Hi everyone, I have a unit price table as follows:

I need to calculate month to month price movements (%).

I have 3 main product groups with a few subgroups.

Column sections present last year months.

The main issue for me is that some products weren't sell in 2 consecutive months.

Another possible problem could be that in one month could be a few sales of the same item.
That means I need average unit price on particular month.

I tried with various posted solutions but nothing have been seem working for me.

Thank you in advance for help!