Nukes themselves are really cheap.
How would you measure this? Maintenence? Opportunity cost? Market value?
Let's hope no one gets nervous enough to try a pre-emptive nuclear strike on the US.
I
strongly doubt that this is the case. There are five legal nuclear powers. Three (America, UK, and France) can be ignored. That leaves us with two: China, and Russia. Based on news reports, China is actually surprisingly happy with Trump thus far, showing himself as a man they can deal with. They talk in terms of money, which Trump understands. I'd be more concerned he tries to sell out the Koreans or something, honestly. The Chinese are adept at soft power, and have shown themselves to be reasonable, if increasingly assertive in their backyard and across the globe. China and Trump will not get into a nuclear standoff unless North Korea falls. Russia is interesting because no one knows what's going on between DC and Moscow. From a practical POV, however, Putin likes deniability. Nuclear exchange is not deniable. And given NATO on the Russian border, surely he's mindful of the risks of direct military confrontation.
There are also the illegal nuclear powers. India seems unlikely to do so out of the blue. Pakistan seems unlikely for similar reasons, as well as the fact that if they use a nuclear weapon, India is likely to respond (same goes if India uses it). Either way, Pakistan is not actually able to launch a strike against the US, because it's range is limited. Wikipedia states that their limit is 2750 km, which isn't enough to hit Hanoi, let alone Los Angeles. There's Israel, but... it's Israel. Israel is not going to nuke its patron. Either way, Israel needs to conserve its nuclear weapons to maintain the ability to use the Samson Option, which would become a very pressing issue if they attacked the US. Finally, there is North Korea. North Korea is probably not able to launch a nuclear strike against the US at this time (certainly not reliably), and has closer targets anyway.
Given the US operates ABMs, I'm not immediately concerned. It's everyone else who should be concerned.