Photography

Yeah but from what I read, the type without glass is also cheap because of the inherent problems problems with it, like typically cutting off the corners due to the edge of your lens being visible in the view.

I would also mention that there are really cheap teleconverters you can find on amazon and such for around $20 US (the type that screw onto the end of your lens like a filter), which will be a massive disappointment. These are never actually made for telephoto lens, so like if you try to couple one of these teleconverters with a 200mm telephoto lens, you'll never actually be able to focus your shot. Just don't even bother with these, they are a complete waste of money even if they claim to work with a telephoto.

On the other hand, there are teleconverters that mount between your camera and lens, which have their own glass in them. For the price OP quoted, this is most likely the type they found. This is like a second stage of lens, and you'll find a good one will not only focus perfectly without bringing the edge of your primary lens into the shot, but they also tell the camera about the change to the focus range and any other parameters so that the camera can properly adjust the shot and the EXIF data is correct.

With that said, $548 still seems really extreme? I have a Canon camera and I found a really good quality doubler on ebay (used) for $100 with Japanese glass which looked brand new when I got it. I use it with my 300mm lens to take pictures of the sun and moon, and cannot tell the difference between images with and without the teleconverter because it focuses so cleanly. Since OP mentioned this is also a new camera, maybe it's just too new and nobody has had a chance to make aftermarket products for it yet, or the used market doesn't exist yet? My camera is over 10 years old so there's a ton of cheap items available.