Set up custom “tiles” for 99c, €1.99, €2.99, €3.99,€4.99,€9.99 etc. on the POS, each of these would be a product.
A variable product price named “2nd Hand” where we can add an amount in ourselves. Also a tile on the POS but with a price that can be entered manually.
This may not be helpful as it isn’t something I do myself and do not have POS…however, do you know about creating custom orders? You are able to create a draft order from within admin which you can either attach an existing product or “Add custom item” - give it a name and set a price.