The USDA claims tomatoes cost from $0.92/lb (canned) to $3.29/lb (grape and cherry tomatoes) on average at retail [0]. No idea what retail produce margins are like, but even if we assume they purchase at 10% of retail cost, that's approx $200-740 per tonne revenue to the grower.
If you assume its towards the higher price, and the grower sells at 10% of retail, that's over $1 billion over 10 years (the length of their contract).
Those are US prices. Australian prices are much higher. And as you cannot store fresh tomatoes, importing them is costly so that prices vary a lot.
As said in another comment, they'll sell them at CostCo for A$7 per kilo, which seems to be a competitive price in Australia.
I think they are taking the worst case there, and the amount going to distributors is highly variable depending on the the food itself. If you google around, you should be able to find graphs of various products (probably including tomatoes).
If you assume its towards the higher price, and the grower sells at 10% of retail, that's over $1 billion over 10 years (the length of their contract).
[0] http://ers.usda.gov/datafiles/Fruit_and_Vegetable_Prices/Veg...