I realise I'm very late with this, but that figure is so low as to be absurd! If she can knit a pair of knee-high socks in 5 hours she must be the fastest knitter that has ever lived, or must be using chunky yarn.

I also knit kilt hose on commission, and I charge $200-300CAD for a pair of argyl hose. I am a speedy knitter, and I make them out of fingering weight yarn on size 2.25/2.5mm needles. It usually takes me about 30 hours to complete a pair (and since I am a full-time student with another job, I usually give people a delivery estimate of a month and a half, so I can order the yarn, knit them, and ship them.)

I know you say she can do them very quickly, but I honestly don't think it's humanly possible to go that fast. I am neither an inexperienced nor a slow knitter, and I am baffled by this.

Argyl is a little more complicated and time-consuming than stockinette with a decorative top, or even cables, but your friend is still undervaluing her skill and her time.