I bought a bowser, wedding amiibo to find purple coins with. I don't know when I'll get it, but I was exploring the sand kingdom for about an hour. I found all but eight coins. I noticed that cappie will mention purple coins if you're in an obstacle level and have already gotten both moons. he won't say anything if it's an obstacle level you have to go through in order to progress in the game though. then, he says nothing. I'm thinking that's where they are. I saw a video of how it works with the amiibo. a purple vortex appears and you run towards it. it will lead you to the purple coins. it won't show anything on the map though, so you have to be diligent.
like a 250 dollar kit back when DDR4 was Intel only