Actually, I have only just seen this. So if it speaks volumes, it says only the fact that I was distracted from this thread and forgot to refer back. I have adhd. Getting distracted happens to me quite often. 🙃
Personally, I don't think punishment works very well. I only have one dc of my own, but have worked in residential settings with hundreds of teenagers where I have been in a pseudo-parental role, including some pretty troubled ones. In my experience, open, honest and respectful communication is usually far more effective than punishing kids. If you have invested in building a really good relationship, they don't generally want to let you down.
In this scenario, I would talk to my dc. I would highlight how much money I had spent on the holiday on the basis of them having made a commitment to go, and I would ask them to look at it from my perspective and think about how I might feel. I wouldn't berate them, I would just respectfully explain how hurt/angry/frustrated/let down I felt. This is how my parents raised me and it is how I have raised my daughter. I have never yet met a kid who doesn't respond to this approach
If you punish a kid, the chances are that their main focus will be on the punishment itself and not what they did to deserve the punishment. They will often resent you for that punishment and perceive it as your fault for unreasonably exercising your power over them. I'm not saying that is an accurate perception at all, but nine times out of ten, that's how the average teenager will see the situation. The blame for the whole incident shifts, in their heads, over to you. You're the bad guy.
If you are ultra reasonable about what they have done while also giving them an opportunity to calmly reflect on their own behaviour and how it might have impacted on others, then they are able to see much more clearly how and why they were actually in the wrong. Be eliminating the power imbalance, you remove the defensive responses that so often get in the way of kids properly reflecting on their actions. They are able to hear what you feel because they're not distracted by the £700 or whatever that they're now going to have to pay. They recognise that they have fucked up, they feel bad and they learn from it.