In reply to jethro kiernan:
Yes full frame lenses are expensive but for landscapes you might not need the fastest autofocus ever, since trees and mountains tend to move much more slowly that the sports cars etc that the the latest lenses are now designed for. Therefore you can buy secondhand lenses which are amazing and cheap. The 20mm f2.8 is a great start and nice and light to boot. I got mine for £150. A 50mm can be had cheaply too and then you are in business.
I own a bunch of zooms but if I'm out and about in the hills I will often just take these two small primes to keep weight down.
Of course you could get a Sony and then use a Metabones adaptor to use your Nikon lenses.
Without a doubt the best places to buy used stuff are Fixation and Grays of Westminster.