Total Main report with two subreports

I have two subreports on a main report. There are 3 sorting groups: Center,
Facility, Name. On both sub reports in Last Name Footer I have text fields -
txtTotal =Sum([Total Price]). On the Main report, in the last name Footer I
have a text field - txtGrandTotal
=IIf([subrpt1].Report.HasData,[subrpt1].Report!txtTotal,0)+IIf([subrpt2].Report.HasData,[subrpt2].Report!txtTotal,0).
This works perfectly for a total on each name on the main report.

The problem is getting Per Facility, Per Center, and Overall Grand Totals.
How do I do this. I've tried putting a text field in the footer with
=Sum(txtGrandTotal) but this doesn't work. I've tried using the same formula
as in the last name footer and that doesn't work and yes I'm a novice.