How to Return Old Item Stocks?

Hi,

Do you have any suggestion on the best practice to return items to stock after a long period of time.

For example, we sold an item 2 years ago, now the customer wants to return those items to get discount in future purchases, however the cost of those items return to stock will not be as the same cost sold on the original invoice, say the cost of the item is 48k, we sold for 96k, and want to return this item in stock for 17k and give this 17k as a credit to the customer.

We tried to use a RMA-> IR -> CM, however the IR receives the stock back as the original cost and not 17k, we still can give to the customer a 17k credit, but how can we fix the IR to 17k, can we do a inventory adjustment (don't really want that), delete it all and use PO process, discount item, what would be the best way to achieve the correct cost in stock ?