> The incremental value of the first 1000 sq ft is nowhere near as much as the next 1000 sq ft
Note that - intentionally or not - the parent comment said 50% larger and not 100% larger which is what they could buy for the same price if it was 50% cheaper.
That depends on whether you take the "50% larger" as relative to the old size or the new size. 50% of a 2000 sq ft unit is 1000 sq ft, so a 2000 sq ft unit is 50% (of 2000 sq ft) larger than the 1000 sq ft unit. This is a less common usage but makes more sense in context, because having the size increase eat the entire cost reduction is a problem if you're trying to achieve affordability, whereas getting a 1500 sq ft unit for 3/4ths of the old price of a 1000 sq ft unit is hardly anything to complain about.
Note that - intentionally or not - the parent comment said 50% larger and not 100% larger which is what they could buy for the same price if it was 50% cheaper.