Try this:

Add unbound text boxes for the min and max values (in report footer?).  In
the report header's Format event procedure initialise them to zero, e.g.

txtMinFootageLowIcome = 0
txtMaxFootageLowIncome = 0

In the detail section's Format event procedure assign values conditionally
to each control:

If txtMinFootageLowIncome = 0 Then
   txtMinFootageLowIncome = [square foot]
Else
   If txtMinFootageLowIncome < [square foot] Then
       txtMinFootageLowIncome = [square foot]
   Else
End If

If txtMaxFootageLowIncome = 0 Then
   txtMaxFootageLowIncome = [square foot]
Else
   If txtMaxFootageLowIncome > [square foot] Then
       txtMaxFootageLowIncome = [square foot]
   Else
End If

Do similarly for other income groups.

I wish you would have stated how the income levels are recorded... Assuming
you have a field named [IncomeLevel] with values of "M", "L", and "H".
Create a totals query by your "different means" and income level. Select one
column as the Min([Square Feet]) and one as the Max([Square Feet]). Use this
total query as the record source of a subreport placed in your main report.

I missed a couple of lines.  To make each min/max value conditional on the
income level you ned to wrap each block of f code in an If statement, e.g.
for low income levels, if this wewre to be indicated by a value in a text
field IncomeLevel:

If [IncomeLevel] = "Low"
   If txtMinFootageLowIncome = 0 Then
       txtMinFootageLowIncome = [square foot]
   Else
       If txtMinFootageLowIncome < [square foot] Then
           txtMinFootageLowIncome = [square foot]
       Else
   End If

   If txtMaxFootageLowIncome = 0 Then
       txtMaxFootageLowIncome = [square foot]
   Else
       If txtMaxFootageLowIncome > [square foot] Then
           txtMaxFootageLowIncome = [square foot]
       Else
   End If
End If