A Patriot missile - usually priced at about $3m (£2.5m) - was used to shoot down a small quadcopter drone, according to a US general.
The strike was made by a US ally, Gen David Perkins told a military symposium.
"That quadcopter that cost 200 bucks from Amazon.com did not stand a chance against a Patriot," he said.
Patriots are radar-targeted weapons more commonly used to shoot down enemy aircraft and ballistic missiles.
"Now, that worked, they got it, OK, and we love Patriot missiles," the general said.
Recently, there have been reports that some groups, for example in Iraq, have taken to attaching weapons to small, commercial drones and using them against security forces.
However, Gen Perkins suggested deploying large surface-to-air missiles as a defence was probably not economically wise.
"I'm not sure that's a good economic exchange ratio," he told an audience at the Association of the United States Army's Global Force symposium in Alabama.
"In fact, if I'm the enemy, I'm thinking, 'Hey, I'm just gonna get on eBay and buy as many of these $300 quadcopters as I can and expend all the Patriot missiles out there'."
No further details of the encounter - such as where or how recently it took place - were given, but Gen Perkins did describe the party that launched the missile as "a very close ally".
"It is clearly enormous overkill," said Justin Bronk, a researcher at the Royal United Services Institute.
"It certainly exposes in very stark terms the challenge which militaries face in attempting to deal with the adaptation of cheap and readily available civilian technology with extremely expensive, high-end hardware designed for state-on-state warfare."
Mr Bronk also told the BBC that Patriot radar systems, while sophisticated, might struggle to target a small quadcopter effectively.
Patriot missiles were first produced in 1980 and are operated by 12 countries including the US, the Netherlands, Germany, Japan, Israel and Saudi Arabia.
The missiles themselves travel at five times the speed of sound, whereas a quadcopter drone typically has a top speed of 50mph (80km/h).