Any meal you can cook without the Joule using other cooking methods. 8 oz of chicken breast (~$1.50), 6 oz of brussel sprouts (~$0.75), 8 oz of potatoes (~$0.25). That's a $2.50 meal. Add half an onion, some bell pepper, some spices, and oil for cooking and it probably comes out to less than $3.

Of course, those are average food prices in the US so YMMV. If you're in NYC or LA/SF, it's going to cost more than that no matter where you shop.