Have you ever read the history of the Grand Coulee dam? How about the Hoover dam?

Let me give you my impression of "fair share"... 

1. Look up the distribution of national wealth by income level.  I've done it but you need the practice.
2. Figure out what percentage each level controls.
3. That's the distribution of the defense budget that should be the responsibility of each level. 

I think it's perfectly logical to pay an amount commensurate with your share of the wealth.