How successful is NASA's COTS program?

Cots?  Are those beds?
COTS stands for the Commercial Orbital Transportation Services program.  NASA needs to regularly resupply the international space station (those astronauts need to eat).  The USA previously did this with the Shuttle program until it was cancelled following the Columbia disaster. As a result, NASA created the COTS program in 2006 to fund commercial firms with good proposals for the 'routine' resupply of the international space station.

The program is now complete with the SpaceX Dragon and Orbital Sciences' Cygnus graduating from the program by demonstrating they can deliver supplies to the space station.

COTS by the numbers
The Shuttle, it pains me to say, turned out to be extremely expensive.  Over the lifetime of the program, each launch cost about $1.5 billion.  It cost around $20,000 to put a pound into orbit.  In comparison, NASA's total investment in the COTS program is around $800 MM, less than a single shuttle flight.  Now, SpaceX is delivering cargo to orbit for about a tenth of what the Shuttle was, around $2000 per pound ($56.5 MM per trip).

Some might point out that the comparison is unfair since the Space Shuttle carried 5-7 astronauts to the international space station, which obviously need more life support than a bunch of cargo.  Plus, the Shuttle has more storage capacity than SpaceX's Falcon 9.  That's all true.  But we can add all of that up.

NASA currently pays Russia $70 MM to get each astronaut to the ISS.  So say you pay Russia to fly 7 astronauts (7 x 70 MM or 490 MM) to the ISS and then fly two SpaceX Falcon 9 for supplies (2 * 56.5 MM or 113 MM).  That adds up to $603 MM.  If Shuttle costs truly are $1.5 B, that's nearly $900 MM in savings each flight.

If COTS' goal was to reduce the cost NASA pays to get supplies to the ISS, it has been hugely successful.