you're probably looking at $500-$650 for each end. say ~$150
for gears, $75-$100 for install kit, $250-$400 for lock right/
EZ locker/detroit, plus some labor for gear setup and install.
since yours isn't a daily driver you can likely skip the consideration
of the most expensive option, selectable lockers (arb,
electrac, ox, etc.). the detroit locker seems pretty popular for
the rear. for the front some go detroit, or ez locker, or lock right.
I don't know much about plus and minus of those but lots
of others have experience and opinions so I'm sure you'll get lots
of feedback (or try a search on this website and I'm sure there's
tons of old threads discussing locker choices).