Mind-bogglingly expensive, no doubt about that. And that goes a long way towards the question of should we / should't we.
Deployed submarine launch allows independent global deployment, surprise and the potential ability to launch after the home nation has suffered an attack - further enhancing the deterrent / uncertainty effect. You have to have minimum 4 subs, 1 deployed, 1 recovering from deployment, 1 preparing and 1 in deep maintenance. The early days of air launch via the RAF was a perfect con by the staffies at the Air Ministry - the aircraft lacked the range to deliver the cargo to most of the designated targets and resulted in the requirement for manpower increases to maintain security and operation of bases. It was a classic example of the RAF top brass being clererererer than the ARMY and Navy equivalents.
I forget who it was getting hung up about the "...but we'll never use it so it's a waste of time..." argument earlier (pre-shut down.) I'd suggest "use" and "usefulness" are perhaps better ways of thinking about it.
Nobody (sane) wants to USE it, but that doesn't mean it doesn't have a use.
It's also important to take the whole issue within the broader context of how and why it came into being. It would be my view that it has served a valuable purpose post WWII and through the Cold War period. It started to get out of control and was curtailed by the SALT treaties which provided a kind of 'balance' between the US / USSR.
The question of replacement of Trident kind of transcends the political divide - it's bigger than a single party issue and bigger than a single term of government.
I'm kind of relieved that the decision has been made to replace - albeit (along with the carriers) at the expense of more conventional forces.
We live in uncertain times today and certainly don't know what the future holds. Whilst we might all desire global peace and stability, i think we are better to walk quietly and carry a big stick.
Chairman Corbyn's obvious and declared inability to say he would be prepared to press the button if necessary kind of undermines the usefulness of the system.
In my book, having it (and we are going to despite what he might want) and not being prepared to say you'd use it (even if you don't really mean it) rather undermines the usefulness and illustrates how singly out of touch with reality the man is.
Nobody wants it, nobody wants to use it, but it's here. Having it and telling everyone you wouldn't use it is even more insane than having it.
All of that said, I wish we were in a different place and we didn't have it. We're not there yet though.