If you were living in Melbourne it would probably cost a lot more. I know that up here my weekly food bill usually exceeds $100, and that's before the current flooding that we just had (bananas are currently running at $38/kg, despite the fact that they're grown in the Tweed Valley, which is only 30km away). A co-worker of mine living in similar circumstances to me has the same comments. I live alone and rarely eat out or order Pizza. I could probably live on McDonalds and get by a lot cheaper, but I'd rather eat decent food and have my fruit and vegetables fresh. Interestingly, I tend to eat out a lot more often on tour, without any real noticeable change in my food bill. Go figure.

Personally, I'm not a fan of living on lentils or dried fruit exclusively. I'm also of the opinion that sampling the local produce/delicacy is part of what makes a tour worthwhile. I ate out almost every day in Japan because the food was just so awesome, and I found it added to the experience of the tour. Really, the OP needs to work this out for himself. Sure, there are ways he can save money, but is he going to enjoy eating the same food day after day?

Really, all this arguing about how much people spend on tour is just a waste of everyone's time (apart from those who want the ego boost that comes with saying "I only spend $1.50 for a year on the road, so I can't understand why all those Africans are starving"). What the OP really needs to do is go on a shorter tour of a few days (or maybe a week), and learn from experience what his food bill is likely to be when on tour. Of course, he'll also learn a few other things that way that will benefit him on the big tour, too.