There was a recent story about a guy using Apple AirTags to effectively track down his stolen scooter. They retain for US $29 each, but you need a compatible Apple product (phone, computer etc) to use them. No monthly fees.
Similar product is the Tile, which will work with non-Apple phones. However it does have some yearly free if you opt for the Premium service that extends the network for tracking / finding your stuff. Even paying for this, your network is going to be much smaller than that provided for free with the AirTags.
Both the Tile and AirTags rely on a peer-to-peer network of connected tracking tags, phones, computers etc. For Tile, this network consists of people who have downloaded and activated the Tile app, where’s for AirTag, every Apple device is automatically on this network, making it much larger.
I would personally go for the AirTags, if you own an Apple device. Way better value and already proven effective by this guy (who has some tips at the end of the article on how to make them work even better).