Latest Month value

You'll need to write a measure to handle this.  

Here is a simple way to do it:

Use a calculated column to get your month date.  This would be something like:

MonthDate = DATE(YEAR([DateField]), MONTH([DateField]), 1)

where [DateField] is the name of the column that holds the finacial details date.

Next create a measure that does this:

Last Month Sum = VAR endDate = LASTDATE('YourTable'[MonthDate])
END
CALCULATE(
	SUM('YourTable'[BudgetValue]),
	'YourTable'[MonthDate] = endDate
)

Please note that this measure will take into consideration the context of your report filters.  If you use a Date slicer and contrain the report, the last month will always been the last month within your Date contraints.