If you re-arrange your From-To charge table slightly you can use an approximate match to find the correct charge. Have a look at Example 1 here:
http://colinlegg.wordpress.com/2012/...-with-vlookup/
That example looks up grades by percentage, but it's the same principle.
The only reason to use SUMPRODUCT (or equivalent) would be if you want to calculate multiple charges and sum them in one go.