Cumulative total with multiple item and time

bryanrendra , Try one of the two

DropPrice = 'Table'[Original Price]+CALCULATE(SUM('table'[IncrementalPrice]),
filter(
ALLSELECTED('table'),'table'[Date]<= max('table'[Date]) && 'table'[item] max(='table'[Date])))



DropPrice = 'Table'[Original Price]+CALCULATE(SUM('table'[IncrementalPrice]),
filter(
ALLSELECTED('table'),'table'[Date]<= max('table'[Date]) ))

I have copied your sample data as a new table named "Pricing" 

Table Name : Pricing

Added the following Calculated Column

Updated Price =
VAR OriginalPrice = Pricing[Original Price]
VAR CurrentItem = Pricing[Item]
VAR CurrentDate = Pricing[Date]
VAR CumulativePriceChanges =
    SUMX (
        FILTER (
            ALLSELECTED ( Pricing ),
            Pricing[Item] = CurrentItem
                && Pricing[Date] <= CurrentDate
        ),
        Pricing[Incremental Price]
    )
VAR UpdatedPrice = OriginalPrice + CumulativePriceChanges
RETURN
    UpdatedPrice

This gave me the following Result.