Almonds really aren't expensive on a per calorie basis. They are far cheaper than tomatoes. For example at Walmart as of today I can buy 2,240 calories of blue diamond almonds for $6.98. The cheapest Roma tomato is $0.44 per item, which is roughly 35 calories. I'd need to buy 64 tomatoes in that case, which would be a whopping $28.16. Something in your math does not add up.

From what I can gather a single tomato uses on average 3.3 gallons of water and a single almond is 1.1 gallons. That is 35 calories vs 7 calories. It comes out to 10 calories per gallon vs 6 calories per gallon which is not nearly as bad as your example. I'm not saying these numbers are 100% accurate, but I'm very skeptical it is 4 times as much water.