A few years ago I tried a number of different chains under similar conditions: SRAM PC-1, Connex Wippermann 108 and 1Z1, and several different KMC. The life was determined as when they reached > 0.8% stretch.
The Wippermann chains outlasted the others by three to four times the distance. The worst was an expensive very chunky KMC which couldn't be split with standard tools and lasted ~ 800 km.
I use Wippermann 108 exclusively now, the nickel plating is pointless under a liberal coating of oil. They have bushings so can be very noisy on a worn cog until they bed in.
Having said that, you can usually pick up KMC S1 for £3.50 so it's more a case of how frequently the chain needs replacing rather than overall cost.