The quiet no and the counter-offer
Once you've got the price and decided you wouldn't have chosen it, there's the saying so, and the saying so is shorter than you fear.
The quiet no. "I'll skip this one, have a great time." Nine words, no reason given, said warmly. Not "I can't afford it", which invites a discussion of your finances. Not "it's a bit much, isn't it", which invites the table to defend the price. Not a speech about priorities. A person who says "I'll skip this one" and moves on to asking about the venue's dog is a person who's declined an evening, and that's all they've done.
The counter-offer. "I can't do Lisbon but I'd love to do the day in town." "Can we do the corner place? I've been wanting to go back." "Shall I just get mine? I only had a main." The counter-offer keeps the people and changes the price, and it's the single most useful sentence in this book, because it's the one that moves the pace for the table rather than just for you. Make it a proposal and not a complaint. Offer the cheaper version as a thing you'd like, because you would.
Once. Say it once. If the table says "no, let's do Lisbon", then the quiet no, warmly, and that's the end. Don't campaign. A counter-offer that's repeated becomes a position, and positions at tables are what make people the difficult one. One offer, taken or not, and then you're either in at a price you'd have chosen or out with your evening.
No speech about money. This is the rule that makes the rest work. The moment you explain, you've made it about your finances, and the table will reassure you, or argue with you, or feel judged. Nobody needs to know why. "I'll skip this one" is a complete sentence and it needs no footnote.
Paying for what you had. At the bill, if the split arrives and you had a main and a glass, "I'll just put in for mine, if that's all right" is fine. Say it as you're getting your card out, not as a debate. In my experience it's followed within ten seconds by someone else saying "actually, me too".
The round. Buy your round. That's generosity and it's the fabric of a pub. What you don't have to do is stay for six rounds to keep up with a table that's drinking six. "I'm off after this one" is a quiet no with a pint in it.
Expect relief. Not always yours. Theirs. Chapter 19 said there's always someone at the table who couldn't say it, and the counter-offer is the door they walk through.