6WB retrofit isn’t that difficult. The biggest part is making sure you buy a cluster that is either brand new or has been properly cleared, as once it is paired to a car, it is locked unless someone clears it with special tools.
You can find the cluster on eBay by searching for “G30 6WB” for around $1100 for a new one. The only other part you would need is a new trim piece which is part #51459387222.
For install and coding, read my
diy here from when I retrofitted it to my G01 X3. Process is pretty much the same for the G30.