This is a bit self delusional. "Use your opponent's strength against him", sway pools to support your cause. Or better yet: start pools with possibly negative profit. Pay-per-share but you payout a tad more than you actually could. That way people will consider your service the most profitable, ergo the best, and flock to give you shares at an extremely discounted rated (it only costs you whatever you add to it).

Better yet: force existing pool owners a: out of business, b: to support you!

Better yet: subvert pool managing computers! Make the machines support you! Or do MITM attacks to get the shares instead of the pools!

Maybe just subverting the developers (enough are US based, hint hint) to write a teensy exploit.

Just cracking the central exchanges and everything that accepts Bitcoin will also cause a rather big stir. A small division breaking into bitcoin-accepting services and selling the bitcoins will lower the price directly and decrease trust significantly.

Visa and Mastercard not providing services to Bitcoin accepting customers would also be quite effective.

Bascially, the cost is lower legally than it is otherwise. And a 51% attack can be solved with a trust model, should people wish to do so.

Lastly you must imagine there's plenty of computing power available to most governments on that list. Temporarily using that power for the time of the attack is a fairly good idea (depending on what you want to do with a 51% attack), and not the full price at all. A cost/hr would be much more useful (imho).