Hard to say, differs a lot. Certainly much better than in Namibia, but it largely depends on the company you fly with. You will find anything ranging from the ubiquitous "Will fly for food" deals where your work your butt off to $5000 dollar deals where you're pampered with hardly any flying. Housing and other allowances can differ largely, too.
I reckon the average is probably somewhere between $2000-$3000 gross.