Editing live shipping rates and deducting specific amounts

Hi,
So I've got some clients who, for some reason, want to deduct a specific amount of money from shipping depending on which product is ordered. For example, they want to deduct three dollars from a tea set or 5 dollars from a computer, etc.

They also want live shipping rates coming from UPS and USPS. I've been checking out the UPS module and it looks like the rate quote is stored in an array with two keys: one for method and one for cost of method.

Is this right?

I'm also guessing that since it uses list() to generate the contents of the table, the values aren't stored (even temporarily), just queried from the UPS API
when the user clicks the "continue" button and THEN stored, am I correct in this assumption?

I'm learning PHP but I've got a programming background so I'm pretty good with this sort of stuff, but I'm stumped.

If anyone can help, you have my gratitude.