My flight cost 1100$ CAD (back when the dollar was low so like 1000 US maybe?) and that was after tax, from Vancouver to Tokyo in May (I thought I got a good deal but my teacher was like what?? You can get them cheaper than that). I took a picture of a for sale sign of an Ayu concert ticket for 6000 yen at one of those shops...
And if it's an artist you really like, and as big a production as Ayumi puts on, I dont think being far away from the stage would ruin your experience
I saw Robbie Williams in Germany with 80,000 others and he was just a speck on stage (though there were massive screens) and it was the best show just because I love him (even though it was sprinkling rain and it was sooo chilly and windy).