How do I return the first value by order (ignoring blanks)?

You need to apply FIRSTNONBLANK to the date. Then use that date as the filter to get the price at that date.

Also look into FIRSTNONBLANKVALUE - that might save you a step.

Or use the pedestrian way

22 Price = 
var m = min('Table'[Modified])
return CALCULATE(sum('Table'[Price End P2]),'Table'[Modified]=m)

Hi Anonymous 
Please refer to sample file with the solution https://www.dropbox.com/t/0WkCrxsXlYxewGbb

22' Original Price = 
VAR CurrentIDTable = CALCULATETABLE ( Data, ALLEXCEPT ( Data, Data[OriginalID] ) )
VAR NonBlankTable = FILTER ( CurrentIDTable, Data[22' Price] <> BLANK ( ) )
VAR FirstRecord = TOPN ( 1, NonBlankTable, Data[Index], ASC )
RETURN
    MAXX ( FirstRecord, Data[22' Price] )

Thank you so much, @tamerj1

It works perfectly and it is exactly what I needed.