Sigma, Tamron and Tokina all have some really great lenses these days. They are every bit pro quality and sometimes test better than the equivalent Nikkors, but offer a more attractive price if the Nikkor isn't affordable. While all my current lenses are Nikkor (35mm 1.8G, 50mm 1.8G, 85mm 1.8G, 24-120 f4 and 70-200 f4) I'm seriously considering the Tokina 16-28 f2.8 for a super wide angle option. And it's about half the price of the Nikon 16-35 f4.
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The most expensive tool is the one you buy "cheaply" and often...