When is an $8 refund no longer worth pursuing?

The retailer agreed to refund $8 for the wrong notebook it sent, provided I return it. The quoted return postage is $6. I'd also need to pack it and take it to the post office.

I've already spent forty minutes explaining the mix-up. My partner says to keep the notebook and stop losing an evening over two dollars. I don't want this particular notebook, but I also don't want the company to benefit from making a small problem tiring enough to abandon.

I haven't checked whether there's another return option. I'd like to ask about prepaid postage before deciding. The practical refund on offer would leave me only $2 after the stated postage.

Would you send one final request for a prepaid return, go ahead for the principle, or walk away? I'd like a way to stop that doesn't feel like admitting the original mistake was acceptable.