It would probably be cheaper for the would-be tyrant to just promise $5000 to each of the poor people (not necessarily in cash - i.e. "if I am elected I will institute a new support program for the people with the budget of $5000 per capita", etc.) - that's how it is done nowdays and works quite frequently.

Additionally, the $5000 per capita program can be financed with budget income and not private cash, making it virtually free for the would-be tyrant once he's elected. Of course, the budget is limited so you have a cup on how much you can offer, and people more adept in economics would figure out it's ultimately their own money that they are being promised, but usually the margin between competing politicians is small enough that people who would vote on the promise of getting "free money" have a good chance to tip it over.

Two wealthy would-be tyrants taking the same position on a view would only require a combination of 10,001 votes, at a combined cost of $50,010,001. And it only goes down as more wealthy people decide to vote in the same way.

It also seems really quite repugnant to tell people "your vote was overruled by one wealthy person, but it's ok because here's some money!" Why should being given some money automatically be assumed to make up for the fact that someone else was able to overrule your vote?

But it only grows with the square root of the number of wealthy individuals. See the paper with Posner; we go through many such calculations: http://papers.ssrn.com/sol3/papers.cfm?abstract_id=2343956

A bit offtopic, but what's your (or the field's) take on buying/bribing/bullying voters?

Even if 10 000 poor person just needs to amass 10K USD, a sufficiently brazen party can just organize for 10 000 other easily mobilized people to vote against the other poor folk. (A common theme around the smaller villages here is the election day free meals, or course the place in full party colors to remind the people who to thank for.) Or is this not so common/significant in practice?)

And so? My $100m made me lord tyrant ruler of the universe. Is existing inequality enough that quadratic voting realistically dismantles rather than reinforces existing power structures?

Has QV been used in any practical context? If so, I'd welcome replies as I didn't pick up on this.

Your $100M got you 4 years in Congress. Let's say you can pass a key bill that'll make you more than $100M. It had better not piss people off very much, because in the next election they'll buy TWO votes each and you'll have to spend $400M to keep your law in place. In the meantime, all those poor people you outvoted are $50,000 richer.

The interesting thing about this is that the more votes you buy, the more you fund your political enemies.

No, you miss the point.

Being $X richer is now meaningless. Whoever is in power controls the currency and the time value of money sufficiently that they can manipulate the next round of voting.