Waterfall chart start valu

Hello

I am attempting to use PBI waterfall chart to show begin values, changes = that add up to the end value.    My base measure is Cost$/unit, which is an annual value.    For example, 2018 $/unit = $400, and ending value 2019 is $525/unit,    I do have a measure reflecting the YOY change by ledger - but would now like to transition to a waterfall chart, with the inital bar = $400, and then with all the +/- end up at $525.   I have a year slicer, so the starting point would be selected value - 1.

There are multiple similar questions already posted - with one solution being a measure.  The other responses are purchasing a commercial visual (probably not likely).    The solution with a measure assumes the initial value is in the dataset - I was unable to make work, as the beginning value was included on allowed dates within the slicer.   My initial value is prior years calculated $/unit.   

Appreciate your reponses!