If you assume the average for those over $100k is $17 billion, capping it at $100k would save the entire budget many times over! $200k is a completely arbitrar

If you assume the average for those over $100k is $17 billion, capping it at $100k would save the entire budget many times over! $200k is a completely arbitrary assumption. And if your cost savings are off by an order of magnitude, it is basically insignificant, at <1% of the budget. If you can wave a wand and reduce benefits, targeting only the top 2000 is probably not the most effective use of your magic.