Easiest and cheapest way to return a package to hong kong?

I ordered an iPhone 5s case by mistake and I need a 5c, the seller said I have to pay return shipping and the package is literally 0.06 lbs, I looked on the USPS website and I've gotten options of over $20, I payed only $8 for the case! (I live in the US)
Any suggestions?

For $8 just forget it. Buy another one and sell your current one as a brand new one.

Skip it = simple.

is NO cheap wy

Kiss the $8 goodbye and pay more attention next time. Lesson learned.

If you realized your mistake before you opened the package, you can simply refuse the package (mark: return to sender/package refused). Otherwise, there's no possible feasible way to return it. If it makes you feel better, I made the EXACT same mistake ordering a case on Ebay (order a case for a 5s, needed a 5c case). I just sold mine on Craigslist for the exact same price I paid.