As long as you're eligible for the fare, qunar should be fine--lots of people use them (though tends to be Chinese speakers/readers as qunar isn't geared for English language or international processing support). Just make sure you make your decision based on the complete "all-in" price with taxes, fuel surcharge, etc. included. I can't possibly believe that 480 RMB price to Nagoya is all-in!

ETA: I have no knowledge of how qunar's after-sales support is, in case you need to cancel, make changes, etc.