Ok, here's the cheap, and yet still very effective, way to do your belts:
1. Get them out of the car and disassembled.
2. Put them in the dishwasher. No soap needed as I understand it.
3. Go to the grocery store and buy a $3 bottle of instant shoe polish (if you need black belts - can't recommend this for any other color). The liquid polish with the sponge on the end. Use the polish on the belts and on the black plastic. THE BELTS AND BUCKLES WILL LOOK LIKE NEW.
I've done this on my belts with only 1 negative - I didn't wash one of the belts and that's the only one that the die comes off of. I know others here have done this also, similar posts happen every year.
C'mon, give it a try - what have you got to lose?