ps. I reject the premise about the cost of the best optics. It pains me to say it, but the best optics -- in terms of performance on ultra high-res digital cameras -- are, imho, the newest lenses, largely irrespective of price. The new 50mm f1.8, 28mm f1.8 and 85 mm f1.8G lenses on Nikon are both value priced and superior to their faster counterparts (or at least equal). The new 24-85 kicks the crap out of the doggish (and expensive) 24-120mm. The 30mm Sigma adds what, less than half the price of a sub-$1K camera, and it's as good as it gets.
I don't think that performance equals price OR theoretical performance measured on a traditional optical bench. The best lens is the lens designed to match the needs of the sensor it serves. My limited knowledge of optical physics kicks in at this juncture, but my experience tells me that the Leica lens that brought me closest to heaven (the 75mm f2 AA) was mediocre on the Fuji Xpro1. Why? I do not know. The same was true for the 24mm f3.8, another blow-the-doors-off lens. Brilliant older Nikkors have given me similarly unsatisfying performance on the D800E. I don't think I am imagining this. (And the sentimentalist in me doesn't like what the empiricist in me perceives, so this is not a case of preference-error).
We live in interesting times. If you can afford it, get the newest upper-grade glass. But you don't need to break the bank. If you are chasing the golden megapixels, hand-held is over, f16 is over, and your favourite MF lens can stay at home.
Of course, our art often demands that these rules be broken, and so broken they shall be.