Welcome to the forum!
If you can get the engines rebuilt for $2K there are quite a few of us who want to know where you did it! The cheapest we've seen is $5K and you have to remove the motor yourself, usually rebuilds cost $10K or so (diesel engine). $2K is a bargain!
As for needing a rebuild - the petrol cars are pretty solid, they're V6 engines so they aren't working as hard as a 4cyl petrol. Diesels should last longer than petrol because they're built more solidly, but other issues cause engine failures, like timing chains (replacement chains about $1.2K, labour about $600-$800 - maybe you can see why a $2K total rebuild seems so cheap!).
A high-km car will likely have other issues to attend to than the motor - steering, suspension, driveline (diff bearings, transfer case bearings etc). None of them should be seen as deal-breakers because they're all easily replaced and once done, gives you a nice strong car. Gearboxes are generally strong but some older auto models (2007-early 2009) had issues with the torque converters that should have been fixed by Nissan although it seems a few have slipped through the cracks. You'll spot them - drive it at about 90km. As you (mildly, not flat-to-the-boards) accelerate past 75km/h the car should start vibrating and this should stop at around 90-95km/h as the TCC finally engages. If that happens, the gearbox needs some work - it should cost about $2K+ with parts from Wholesale Automatics in Vic.
Good luck with your search!