Honesty is extremely important in a marriage. Especially since you know that this very thing is something so upsetting to him in the past that it prevented him from going and having a good time -and that it would be construed as lying, that it's a deep rooted problem from his childhood; I can't think of a single way you could tell him that would go over as a positive to him. It's possible that I'm wrong...but no matter what, if he got upset about things like this before, you run the risk that he will be upset about it again.
Return the trip and decide on a trip together. Six hundred dollars is a lot of money, and it's his money too. These are the kinds of decisions you should be making together. You two are a partnership, and in order for both members to be happy, things need to be decided on together.
If you feel that all your money, time, energy, ect goes to the children, or that he doesn't give you any attention, love, or whatnot, and that you need a vacation or some time together, that's something you need to discuss with him. If he refuses to listen, perhaps the problems go deeper than you think. Marriage counseling can work wonders, and it isn't just for people who are on the brink of divorce, sometimes it just makes a good marriage even better.