Cheapest flight HND/NRT-HKG... Japanese travel agencies?
 

I'm trying to get a decent price for a one-way nonstop flight from Tokyo to HKG on a weekday in March. Booking online only yields exorbitantly priced flights >$500. I am currently in the US. Would it make sense to try to buy this ticket from a Japanese travel agency once I am already in Japan?

wow that is insanely expensive.. try some of the chinese travel agencies. just hop on yelp and type "chinese travel agency"

here's a website i usually check:
http://his-usa.com/ja/top/Top.aspx

the ticket should be closer to the 250-300 range especially on a weekday.

My simple answer is NO.
One-way oversea tickets originating from Japan are always extremely expensive, especially when you buy them in Japan. on the other hand, NRT/HND-HKG round trip ticket are usually quite cheap. You should try to make a round trip itinerary or open-jaw itinerary.

Travel Agency
 

I went to Japan in May 2009...

I am not a big fan of big tour groups, so I was excited to find Esprit Travel

http://www.esprittravel.com/independentjapan/local.html

We told the travel agent what we wanted to see...she also had a variety of suggestions. We were given an itnerary to follow (if we chose to). They arranged all of our trains and hotels. We had a personal tour guide for 1 day in Tokyo, and a personal tour guide for 1 day in Kyoto. It was the perfect trip. No pressure to follow the herd...

The tour guides gave us opportunities that other travel agents didn't offer. I know this from talking to people we met at dinners and bars. Everyone wanted to know the name of the travel agent we used. For example, in Tokyo, we had the usual sightseeing of the Fish Market and temples. But, our guide arranged for us to have a blessing at a Shinto Shrine. It was VERY cool. In Kyoto, we spend a few hours with a calligraphy master in his home/studio. We also had a private tea ceremony with the abbot of a Zen Buddhist monastery.

Basically, they will build the trip you want. You just tell them what you are interested in doing.

I tried to book on Cathay Pacific Japan Site for ex-NRT and it shows a round trip fare of 45,400 JPY on random days of March, you can simply dump the return segment.

This is an outstanding route to use NH points for a free ticket -- and if you have Amex membership rewards, you can readily convert them to NH points. In the past, I've gotten value like 10 cents a point on this route. NH lets you book one way award tickets, I am pretty sure.