I am about to get a 6-card (sapphire R9 280x) rig put together this week, and right now am looking at about $3900 for all the parts (cards, risers, frame, corsair 1200i +850w PSUs, etc). Is this a good price, or should I be using a few lower-budget items?

Trying to figure out what the $/kh ratio is that people are looking for when they build a GPU farm.

also: is GPU mining going to be dead in 3 months when scrypt asics become the next big thing (gridseed is close, they just need to make a 40-chip board rather than the hokey 5-chip cylinders that cost more per khash)? or will there still be good profits in mining?  I am just worried that I will put $400 into it, make $1000 [profit] in 2 months, ASICS will come out, and I will make another $1000 in the following 3 months, then by the end of 6 months GPU mining is obsolete and I am left with a rig that has little if any resale worth.