Based on JBA pricing... probably $6k...
That's why im curious to see exactly what he's doing for the 6" lift. If he's just adding coilovers, control arms, shocks and a spacer or longer springs in the rear that could be accomplished today:
Superlift $2000
Custom length KING coilovers $1700
JBA UCAs $450
Rear shocks $150-$400 depending on basic shocks vs resi's
Rear spacer $150 (if you just buy an RC kit and use the rear spacer only)
TOTAL = ~$4700 if you go with resi shocks
Since JBA priced his coilovers at $2500 instead of the $1700 custom length KING's, that's another $800 easily right there putting. Plus he currently charges ~$270 per shock... so that's another $140 more based on his current pricing. So the total could easily be ~$5650 not including any other additions he puts into it.
At least someone else is making stuff for us! Expect prices to be outrageous until lifting XK's and WK's becomes popular enough to elicit suspension lifts from Rancho, Skyjacker, BDS (improved version, not cancelled version), etc.