As far as I know, you cannot easily extend the PriceDetailValue class just like you can with meta data plus.
You can do it but it would mean rewriting some of the sub systems. For example you'd need to extend PriceDetailValue and then you'd need to write your own implementation of IPriceDetailService and the class responsible for saving to the database. Seems overkill based on your initial question.
I'm wondering if there's a way to create extended fields for PriceDetailValue. I can implement extensions for IPurchaseOrder or ILineItem, but not for IPriceDetailValue.
Can we extend or create custom fields for this?