The only two airports in Tokyo are Haneda and Narita. You're most likely going to fly into Narita airport, which is about a good 1 hour from Shibuya. First you have to take a train from the airport to Tokyo station, of which there are many options but range widely in price from expensive express trains to public trains which take a long time. From Tokyo station you have a few more options via public transit to make it to Shibuya. But, as for Shibuya, it does not have an airport it's just an area of Tokyo. You'll almost certainly be landing at Narita, as Haneda is international but I think serves the rest of Asia moreso than the West. As for pricing, its generally $1000 for a round trip ticket and that really doesn't fluctuate very much aside from increasing during holiday seasons. September is generally slow so you can expect to pay around that much.
As for show tickets, in Japan show tickets are usually sold at local convenience stores via automated kiosks, where you make an order, print the receipt, show the receipt to the clerk, and then pay for the tickets and receive them a few mins. later. There are also event desks much like a Ticketmaster where you can get tickets for various events.
After a quick google search i found these:
fdjp.com
http://www.s-ovation.com/event/english/index.html
http://www.coasttocoasttickets.com/
Perhaps one of them can get you tickets somehow. You'd almost certainly need to pay upfront with PayPal or a creditcard I'd imagine.
Finally, as for currency exchange, any large bank can do the exchange for you. Japan is a cash society and foreign credit cards don't always work, so you'll almost certainly want to purchase some Japanese currency. Again, any large bank will handle that for you, you don't have to be in Japan to do it.