You would definitely not expect that a machine selling for $1000 would have used more than $1000 of energy in its manufacture. Even accounting for energy costs all the way down the chain (materials arguably don't have any other cost other than energy and attention involved in collecting/isolating/refining them), my uninformed guess would be that with something like a computer, it's something like a bit less than half, with the rest of it being amortized human attention at various stages plus some profit margin, though I'm sure there's more refined and accurate models available.
So, throw out $480 as an energy number for our $1000. That means old hardware that's less energy efficient to the tune of $40 a month will out-impact the manufacturing cost of the new machine in a year.
As an exercise, contrast this with older automobile. If you've got a well-functioning 10-20 year old vehicle, it's probably somewhere between 80% to 50% as energy efficient as the higher efficiency choices you can buy new off a lot today. But the sticker price of a vehicle will tell you that it probably $10-20k of energy to produce. Because that number is high, from today, it will probably take your used vehicle longer than its remaining lifetime to exceed energy use involved in making the new car (and most new vehicles won't get you where you're going any faster either).