Well, North Korea has shown that you can still develop nuclear weapons with a shoestring economy and near constant famine, so the economic factor isn't as big a hurdle as it once was. If we're not willing to use diplomacy, the only other option to prevent nuclear proliferation comes down to espionage or force, both of which are temporary measures that may face backlash that in turn makes Iran even more determined to get the bomb.
Basically, I'm of the opinion that nuclear proliferation is inevitable. All we can do is try to slow it down without exacerbating the situation and hope to cope with the nuclear future.
