I just did some calculations, and ASICs might actually be affordable.

Assuming one can sell 500 of them, building a "bitcoin accelerator card" which yields 5 gigahashes might be possible for less than $1000. If one wants to build one big (copacobana/deepcrack-like) mining rig instead of selling cards, one could possibly reach 5 terahashes (and thus attack the network) with less than a million dollars, probably more like half a million. (This beast would contain 2000 chips.)