Welcome to the board. As far as what you care about, i.e. the costs/repairs after 120k the good news is...it depends.
As a start point it is worth noting that the LR3/D3/LR4/D4 platform is light years from the issues experienced by previous generations-so anyone telling you to avoid a Rover at all costs may, or may not, be basing this off a somewhat well deserved reputation for being rather expensive to maintain in many eyes. Keep in mind that the modern Range/Land Rover is an extremely complicated machine-that was true of the RRC in her day, the D1, and the subsequent generations i.e. the Dii, the P38 (avoid!), and the L322 RR.
As it relates to what you are looking at the 'it depends' is based off the simple question of what is its history? A lot of trucks are showing up on small lots that buy from wholesaler auctions that come with minimal history and often less preventative maintenance. That means the initial cost of ownership to get her up to spec may be high.
On the other hand the good news about 120k is most of those things should have already happened and thus have been dealt with! Specifically you should look to see if it has an AMK compressor vice the Hitachi unit (usually goes at 10yrs ~100k miles or so), or if the Hitachi has been rebuilt. The air struts may have hit their lifespan too, likely already, so there is the possibility that those have been replaced or that they may need to be.
Presumably at 120k the LCAs and all the other 'consumeable' items (bushings, brakes) have been done, at least once.
You'll want to check for signs of water ingress in the passenger side floorboard-take the time to pull the carpet up.
Drive it and listen for clunks and the like, usually a sign of the aforementioned bushings going.
A short read but poking around here is a good way to get another like perspective:
http://www.robisonservice.com/servicedep/buying-a-land-rover.asp#LR3
This is the most pertinent part:
Designed from the ground up with a combination of Ford and Jaguar technology these new trucks are by a large margin the most reliable vehicles Land Rover has ever offered.
You get a lot of truck for the money these days but they will not be Toyota like in their ownership relationship. Every Rover has a soul, if that's not something you are interested in dealing with it may not be the best option.
r-
Ray