>The "something" to be manufactured isn't nuclear power plants.
Wrong, actually. Whenever multiple nuclear plants for submarines in a given class are manufactured, the fact that multiples are being built does lower the cost, although most of that is just from having a complete design to use rather than any kind of mass production. Navy reactors aren't really SMRs since they're also old technology, but they're a good example of how much easier/cheaper/greener it is to build small reactors instead of large ones.
> It seems like the 5 GW one might be cheaper.
Small modular reactors typically run up to 300MW in size. There are very few applications for a 5GW reactor. Besides, the costs of the small reactors in terms of time, money, operating expense, security and other things are so much less than for the large plants that the math really doesn't work anyway, even for your extreme example of 1000 5MW reactors.
Wrong, actually. Whenever multiple nuclear plants for submarines in a given class are manufactured, the fact that multiples are being built does lower the cost, although most of that is just from having a complete design to use rather than any kind of mass production. Navy reactors aren't really SMRs since they're also old technology, but they're a good example of how much easier/cheaper/greener it is to build small reactors instead of large ones.
> It seems like the 5 GW one might be cheaper.
Small modular reactors typically run up to 300MW in size. There are very few applications for a 5GW reactor. Besides, the costs of the small reactors in terms of time, money, operating expense, security and other things are so much less than for the large plants that the math really doesn't work anyway, even for your extreme example of 1000 5MW reactors.