Maybe it's just me but IMO a huge part of being 1/2 of a couple is being able to compromise. Also, being a part of a larger group also requires compromise. If it was me and I was being warmly welcomed into a large group of nice people I'd bite the bullet and go along with things. When in Rome do as the Romans and all that
NO flames but here is something you may not have thought about.
Since you can afford to do all this and simply do not want to, because it's just not the way you and your group does things, your decision to not participate will probably be taken by your BF, and all his other friends, to mean that you're just not interested in being a part of the group.
Now, if you really genuinely couldn't afford to participate that would be an entirely different thing. I don't think anyone would read anything into that, but when we opt out just because we want to, well that has consequences. Maybe you don't care about the consequences, but to pretend there won't be any is a bad idea. If these people are a huge part of your BF's life he may only be interested with someone who is able to swim along side him KWIM.