Not exactly your route but for comparison's sake:
Just booked from TPA on UA for about $2100 per X 4 seats. An additional $109-$119-$129 gets the comfort seats, depending on where they're located. It's a grind, though as the way out is TPA IAH SFO HKG and the way back is SGN NRT IAD TPA. We're flying over to SGN from HKG.
You've got to watch out for those sub 1 hour connections offered on the cheapest flights. I noticed some were only 35 minutes. :O If it happens to be a spot where you're going through immigration, forget it.