You'll have to sum the two columns separately. However, you can create a
formula that combines text and values to get what you want. Assume the sum
of the low end of the range is in cell B25 while the sum of the high end is
in C25. You could use a formula along the lines of

="Grand Total: "&text(B25,"$#,##0.00")& " - "&text(C25,"$#,##0.00")

That would display somethng like:

Grand Total: $25,000.00 - $50,000.00