You don’t owe anyone a look at your bank balance to justify skipping a trip.

Once money becomes the reason, the conversation turns into a negotiation, because somebody will offer to cover you, or do the arithmetic at you, or propose a cheaper version. Now you are defending a budget instead of a decision. Not going is a complete answer by itself, and what sits in your account is nobody’s business, including friends who mean well.

Keep a short line ready: that one is not for me this time. Then change the subject. If you do want to go and truly cannot swing it, you can tell one close friend the real number, but choose that rather than get pressed into it.