Depends on where you buy and what country you're in for shipping, etc. For instance, for my Note 3 I got chargers (not receivers) off of ebay for as little as $17.00USD. Amazon has them, too, but may not be available to buy in some countries. Sometimes you can finds specials, too. I paid more for others (business owner here) and less for others with a special. These are popular now so many sites will have them discounted sometimes, depending. Receivers are the other part. Note 4 is not wireless charging ready without either a receiver or a wireless charging back cover. The back covers here are around $30.00 and a good receiver can be had for between $10.00 and $15.00. Fifteen dollars is high. When I had a receiver in my Note 3, I think I paid about $12.00. It died when my battery blew a cell so I switched to the wireless charging back cover.
Long answer. Sorry. Hope it helps.