Internal air tix - I am confused

In one month from now I want to fly from Osaka to Tohoku - preferably Sendai but will consider other point of entry.
Then, in mid October I want to fly from Memanbetsu (N Hokkaido) back to Osaka.

I understand there are discounts apparently available, but all my web searching leads me to full fare tickets, which are not cheap.

I don't want anyone to go web-shopping on my behalf but can anyone help me cut to the chase and find the best deals?

I am flying into Osaka from abroad, but not on JAL or ANA, so I don't qualify for their deals.

Autumn Crew,
check this page if you haven't. You don't necessarily have to be JAL/ANA users.
http://www.japan-guide.com/e/e2364.html

I have looked at that page, and while it is very well organised I found it to be the portal to confusion.

That is, once I followed the links to the actual airlines the discounts seemed to disappear. All of the flights seem to be about Y25-30,000.

I realise that I have more research to do, unless someone can simply let me know that, for example, there is a discounted flight from Memanbetsu to Osaka.

What about online booking sites like Expedia? Are they good for Japan domestic tickets?

OK - Using Ai-something (an ad bannner on the page you suggested) I have booked Osaka to Sendai, on an airline code KEX (I couldn't find what the actual airline name is!).

That was reasonable. All paid for now.

Seeking a Memanbetsu-Osaka ticket Google bumped me to Expedia, who quote $1,200 for the one hour-plus flight!!!

What to do!!!??

This is Panic Territory now.

Thirty minutes later, and I have found my way back to Ai-Ticket, who quote a much more reasonable $250 for the flight.

Well, my query about Expedia is answered!

Air passes - most likely the cheapest option for your itinerary - can be booked through travel agents and airlines in your home country. You will be paying around 13,000 Yen per domestic flight:
http://www.japan-guide.com/e/e2364.html

Maybe that could be spelled out more clearly on the discount tickets page. Or perhaps I have to read more carefully.

In this age of DIY bookings I imagined I didn't need an agent; that I could get the best deal online.

In the end my tickets are not hugely more than the pass. But it was a bit stressful.

And now: on to accommodation and car rental bookings!

I know, I know .... ToCoo! for the car ...