Calculate difference from movable value and the highest

[accessuserit]

i need help to resolve this problem:

i have this field:

id,prod1, prod2, prod3, prod1price, prod2price, prod3price

in the various record, i need to found a predefined product name ( for example car) ad calculate the value difference of field price, respect the high value. If car is in field prod1, here price are in prod1price exc....
for example:
record
car, bike, boat, 10 , 20 , 30 ( the difference from car value and the highest is 20)
record2
house, plane, car, 50, 100, 10( the difference from car value and the highest is 90)

now, i have found the formula to found the highest value.
i need the formula to define which value is combined with car.

I need tocalculate the difference from "car" and the big value, considering that car changes field position in some record.

If you help me, are e very big friends!!!!!
Sorry for my english, and my low know-how of access, but are 20 day that i work with this program....
Paul