largely depends on cost of the box, but you're looking at 3k absolute minimum for that, plus diff, mounts, tailshaft, shift linkage, possibly dccd bits plus labour to install.

This is the approximation I got from stechnic a couple of weeks ago and ASG gave me today, plus someone on here had a 6 speed installed just before christmas for 6k

Smashed my second gear a few months ago so have been looking into it