Yup - LOL, don't buy those!! 
They have come and gone on eBay, and sometimes (I haven't looked for them for many months as I have all I need at this point) they would show up for a reasonable price. But it may be that from this point all that will be availble will be from crazy scalpers like the one you found.
If you do run across some in the future for a more reasonable price (<$30) you might want to grab a few. They are nice little devices:
v2: Do motion and temperature, are very fast, very reliable, battery lasts a long time, and really tiny/easy to "hide"
v3: Do motion, temperature, and humidity, are very fast, very reliable, battery lasts a long time, but are a little larger than the v2
In the meantime the Third Reality motion sensor appears to work well for other HE users, and is much more reasonably priced at $19 - only does motion, no temp:
https://www.amazon.com/THIRDREALITY-Friendly-Required-SmartThings-Devices/dp/B08RRRWK6B
