There's no hard and fast rule for pricing damaged chips. A very very very general view is that a damaged chip might be 'worth' about 30% of the same chip in undamaged condition.

BUT...if the chip is relatively common in undamaged condition, a damaged one would be worth even less.

And...if there's very few of the chip available in ANY condition, the damaged one might be worth more than 30%. It all depends on how many collectors want the chip. Some collectors only want "new" condition chips.

Hope this helps a little