The pro-prop-8 side spent $39M. The passage of the amendment caused the state to stop recognizing 18,000 previously-legitimate marriages. So if you count only immediate effects, his $1000 contribution works out to 0.46 marriages, or destroying the marriage of about one person. Is the emotional harm done to that person worth hundreds of thousands of dollars? It's at least comparable.

In fact I think the harm done to Californians and other Americans by the passage of prop 8 is vastly more than is implied by that simple calculation. I'll just link to my other comment: https://news.ycombinator.com/item?id=7525692