$ per GH/s is what kills hardware mining these days, the sudden price hike has shocked the existing mining community and makes the barrier to entry for mining much greater.
Erupters were $8 ---> now $40-$60 [so from about $25 per GH/s to over $150]
Blades were $250 ---> now $500-$800
[$25 --> $70]
Cubes were $600 ---> now $1100-$2000 [$17 --> $42]
KnCs' were $4500 ---> now over $15k-$30k [$5-$7 --> $50]
etc etc