If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
That would be an effective demonstration of scope insensitivity in an ideal scenario where money has a flat conversion to utility in that range for the individual in question. If $200 is in the subject's budget, but $400 is not, this may be entirely rational behavior. A donation which puts you into debt will have a much more dramatic effect on your own utility than one which leaves you solvent.
You're right, the $200 vs $400 example isn't ironclad -- even a rational altruist will still have a limited budget. The reason I ascribed scope insensitivity to the example was that it's worded in terms of valuing 'saving lives' as opposed to valuing lives, which, as I explain, is a hallmark of scope insensitivity.