With the macbook and gopro there I wouldn't think $15 is that big of a deal. A kid was at the hill on Saturday using a hockey stick to mount his gopro. The time it takes to DIY a pole and the end result isn't worth $15 to me. When you are at home can you re-attach it to the swiffer to get some cleaning done?
You are looking at it the wrong way. Just because you see a couple expensive things sitting there doesn't mean he is frivolous with money. Not spending $15 on something he can make from things laying around may allow him to afford some other nicer things. Don't equate nice things with having money and don't equate having money with being able to just buy anything you want. Most people have money because they don't spend it.