Hi

Using Dependent Data Validation would be a good starting point.

Similar to your existing drop-downs, but they filter out data that does
not fit the previous criteria:

Debra Dalgliesh has numerous examples, this should get you on the right
track as it has step-by-step instructions on how to set it up.

http://www.contextures.com/xlDataVal15.html

Once you have that setup, you can move onto a Index/Match table array to
look-up for your variations in charges.

HTH
Mick.