Cerg and I went to look for a blue suit last Saturday. I wanted an Armani but I couldn't find one which suited my taste (read: none suited my budget), so I settled for a relatively unknown brand.
If you're looking for good yet affordable suits in Japan, you may want to try going to department stores located outside main urban areas. Like me, you may be able to find there suits that will fit your budget.
In case you didn't know, you can have the trousers shortened for free at the department store. Just ask the saleslady when you pay for the trousers and they will fix it within 30 to 45 minutes. If you need to ask in Japanese, try saying "take tsume onegai dekimas ka".
While waiting for my new trousers get altered, we ate crepe at Rainbowhat and bought some chocolates.