If you apply the same anti-consumption calculation to everything in life I applaud you wholeheartedly.
That said, you can buy a toaster oven for $30 from Walmart, and that cost covers the energy, material, transportation, and labour, plus markups at each stage. If you assume a $0.10/kWh energy cost, you might have at absolute most 100kWh of energy used in manufacture. That puts the oven/toasteroven breakeven point from an energy perspective at no more than about 60 hours of heating element usage.
That said, you can buy a toaster oven for $30 from Walmart, and that cost covers the energy, material, transportation, and labour, plus markups at each stage. If you assume a $0.10/kWh energy cost, you might have at absolute most 100kWh of energy used in manufacture. That puts the oven/toasteroven breakeven point from an energy perspective at no more than about 60 hours of heating element usage.