Auto Generate Number based on Selection

Auto Generate Number based on Selection

Is there a way to automatically generate a number within a certain range, in numerical order based on when the record is added? I have an auction item database and I would like to automatically assign an item number to a new item based on what category that item is placed in. Each category has its own range, so lets say the category sports has a range of 100-199. So I would need the first item added to the sports category to be item 101, the second 102 and so on. It is obviously important that each number is unique.

Thanks