Whatever the price is now, you can expect to be less in the future. Ten bucks each (just an illustrative number, I really have no idea) right now because they're made by hand? Could be in 10 or 20 years you'll get 10k units for your ten bucks as they roll off a mass-assembly line.
Moore's Law and all.
Don't think of this as a consumer oriented coin-sized desktop with a popular brand's logon on it that you can carry around in your pocket. Think of this as something you purchase in 40 kg batches, fitted with the sensors you need (light, sound, vibration, chemical, pressure...) that you then scatter about. (Assuming they have wireless connectivity, yes. They'd be useless if you have to run wires to each one to establish communications.) You would simply not care if one is lost forever - you'll just buy another 40 kg batch when these wear out, are damaged, or scattered too widely by the wind. Military, environmental and health monitoring possibilities were mentioned in the article. Vernor Vinge's science fiction novels are the first time I recall encountering the topic, back in the 90s.