Don't rightly know resale values for the newer Exaltas, but 450k is okay for an 03 car I think, too much for an 01, depending on mileage.

For Nissans, check that there's nothing wrong with the Aircon Compressor (they're more expensive to replace if they break... magandang AC kasi) or the gadgets. The bugbears of the Exalta line are usually the electronics or electricals, as with so many gadgets, plus that powerful AC, they sometimes overwhelm the battery/alternator combo (on the old ones, on the newer QG engines, this may not be the case). Check that the car starts up easily, that the interior lights don't dim too much when you turn the headlights or AC on...

Also check the condition of the shocks. Sentras are softly tuned, so the 01' might be a little too soft by now (but this is also just guessing based on the B14 Exaltas... the N16 Exaltas are still very new).

Other than that, there are likely no major problems with the cars... (knock on wood... )