Capturing values at the bottom of a column

I have a spreadsheet setup with columns and monthly a new row is filled out with values. What I am trying to do is capture the sum of the last 6 rows at the bottom of a column. I was able to capture the value of the last item in the column using this equation:

=INDIRECT(ADDRESS(MATCH(1E+30,B:B),COLUMN(B1)))

I was also able to capture the group of six from a given base cell like this:

=SUM(OFFSET(B14,,,-6))

In this case B14 is my base. What I am attempting to do is use the last cell equation as my base but I have not been able to get this to work. My last attempt:

=SUM(OFFSET((ADDRESS(MATCH(1E+30,B:B),COLUMN(B1)))
,,,-6))

Any thoughts on how to get this working. I am very open to ideas if there is a simplier or different way to do this.

Thank you,

-Matt

How about:

=SUM(INDEX(B:B,MATCH(9.9999E+307,B:B)-5):INDEX(B:B,MATCH(9.9999E+307,B:B)))