Let's even be more direct:
Cost of ~3 Mh/s:
GPUs 4 280x at $1200
PSU: $150
MB + CPU: $150
RAM: $40
Extras (3 risers, 1 usb pen or HD) : $60
Total: $1600
Resale value after mining: 50% = $800
Your cost: $3000
Resale value: 0 ?
Of course it takes time and effort to setup and research GPU rigs. It however takes stomach to fork $1000 per Mh/s.
This isn't Bitcoin ASIC all over again. When promoting and saying that Bitcoin ASICs save power and you'll mine for longer, it was a given that they offered 100x + the speed of a GPU. They offered 2 orders of magnitude better on both power efficiency and speed. Scrypt asics provide the same speed at much higher upfront cost. For some reason that 100x vs 1x is only a minor detail in this discussion!