The 7900 outer chainring is probably the nicest chainring ever made and is certainly the most technologically advanced. The Hollowtech II design adds a hollow forged 3D depth to make them incredibly stiff, which in turn improves front shifting due to less flex. The chainring bolts mount from the inside of the crankset giving the crank and ring a super clean look. Other than being completely pinned and ramped for superb shifting, it is heat treated and anodized, then the outer most part of the ring receives additional machining and polishing.
This outer ring is what Shimano calls 'B-Type' meaning it's machined ramps and pick up pins are specifically designed to function with a 7900 39t inner ring. This chainring is not cheap by any standard, but after considering the engineering and workmanship that went into it, you can start to understand it's price and may even consider it a value.