Yea, $100 is kind of a lot, which is why we priced our smart speaker blocker at $40. It's called BuzzOff and is available at buzzoff.info.
With my naive understanding, I was expecting a more generic device that can be placed close to any microphone (laptop, phone, smart speaker, etc) something like this IKEA usb lamps : https://www.ebay.com/c/1278841657
We could make BuzzOff quite a bit thinner, but the Echo power plugs are the limiting factor, they are almost 10mm diameter.