If you got $3000-4000 you're definitely good to go for a week or two, heh.
What I would do is this:
Look up prices for flight tickets to Tokyo.
Look up train costs from Tokyo to Fukuoka, and back.
Google for hostels (cheap places to live) in Fukuoka. Count on 20-30$ per night.
Hostels Fukuoka@google.com
As for the concert tickets, count on 20,000 yen for a ticket and you'll be sure to get into the arena.
For food, count on 10-20$/day you stay.
For public transport, count on 5-10$/day and you're on the safe side.
For shopping, bring as much spare cash as you feel like. This spare cash can also be used if you run out on cash in any of your other areas, such as food and so, but that shouldn't happen if you just stick to your plans, which isn't hard.
The tour items usually range from 500-3000 yen, use
www.xe.com to exchange into your currency.
T-shirt 1,500 yen
Towel 1,500 yen
Light stick 1,000 yen
Uchiwa (fan) 1,500 yen
Maybe there's somewhere you can check up the prices for last tours items, there should be some old thread about it somewhere in the News section.
Unless you give us more exact information you'll have to do the calculation part yourself.