I just picked up a 13 plate with 10k miles on for £7.5k, there was a lot of choice, but not a lot around my area, and given COVID, I had to buy it unseen.
The only pre-requisties I had were the colour (Tuscany green) TA engine, and the winter pack, with the exception of a couple of marks, mine is immaculate.
I think £6k is more than reasonable, just make sure that it comes with good service history and appears cared for inside and out, as you've got a TA already, you'll know all about the engine.
Watch for any difficulty getting the car into gear, the dual mass flywheel goes on these and knackers the bellhousing, it seems this can happen at any mileage, this was introduced on EURO6 engines, bit haven't found out if this is the case on all the 4x4s as mine's a EURO5.
Give the turbo actuating rod a wiggle, on the higher mileage ones these joints wear oval and can lead to a loss of power.
Check for any sighs of centre prop bearing wear (rumbling, knocking or wobble) as this is a pricey bit of kit I'm told.
Thee 4x4 undertray seems a bit hit and miss when it comes to rustproofing, so have a poke around underneath.