Whatever the kind, food that is
local and in
season tend to be cheaper, as they need less transportation fee and is abundant. Plus, they are the most nutritious.
By local I mean from the town you live in as opposed to a prefecture that is hours away by truck. It will also help the local economy and agriculture.
So if you expect to buy European or Southeast Asian food, many tend to be rare and expensive, but for example, right now you can buy various Japanese citrus fruits like mikan or iyokan for less than 300 yen a kilogram.
Once you decide where you live, keep an eye on flyers from your nearest market (be it supermarkets or a shopping street of individual stores). They are available at the stores or you can view them on their websites if they have one.
Here is an example:
http://yorkmart.misbit.com/sale/handbill_img/lMjRfajJfMTI3MzUxXzE0MDMw...Potatoes, onions, carrots are 38 yen a piece if you buy on March 5th.
(Keep in mind that, compared to say U.S. grown ones, potatoes tend to be smaller while carrots tent do be bigger.)
Huge daikon raddishes keep you warm when served hot, and here they are 128 yen a piece on the 7th.
You can look for various chain stores like OK Store which has a reputation for their cheapest prices.
http://www.ok-corporation.co.jp/You can also try to stick to the same family-run store, like vegetable shops or meat shops. In the days of supermarkets, they struggle to gain customers and will often give you friendly advice and discount, especially to frequent customers. Here is an example of a big shopping street in Osaka area, although there are smaller ones everywhere.
http://www.shinsaibashi.or.jp/If you haven't decided which part of Osaka to live in, you should try to choose from the more modest areas as opposed to the high-end areas.
I also hear that Osaka is all about bargaining. While people in Tokyo area don't try to bargain, the Osaka people would bargain at any place they'd go to. You might want to pick that habbit up from the locals.
