The XM25 is a $35,000 weapon that fires tiny little 25 millimeter grenades up to 500 yards. But these aren't just any microgrenades: they're smart microgrenades that can penetrate heavy cover and then explode when they're on the other side.
The XM25's cleverness comes from a combination of a computer in the gun itself working together with a computer in each round of ammunition. If you want to negate a piece of cover that an enemy is hiding behind, a laser rangefinder on the gun sends the precise distance to the cover to the round. When the round is fired, it keeps track of the distance that it's traveled (through some super-secret method of counting how many times it's spun in flight), and when it's gotten just behind that piece of cover, it detonates, throwing shrapnel several feet. The XM25 has been used in over 200 missions in Afghanistan so far, and the vast majority of these have "ended quickly," according to the U.S. Army, which has just ordered 36 more XM25s.
The reason that the XM25 is so expensive to field is the ammo: each 25mm airbursting round (available in flavors including thermobaric, flechette, armor piercing, door breaching, high-explosive airbursting, and even non-lethal) originally cost about $1,000 per shot. This has now been shaved down to just a couple hundred dollars each, but each and every round is still made by hand.
When more XM25s start getting deployed and the ammunition starts being made by robots instead of by people, the price per shot should drop down to just around $25. That isn't too expensive, considering that this weapon is designed to do more with one round than most guns can do with twenty. And any way you look at it, it's way way way cheaper than an airstrike, which up until now, was the most reliable method of negating an enemy hiding behind cover.