Noneedtoworry, I feel your pain, and I can see you're trying to do all you can to steer him back onto the right path.
But can I just point something out: He DID do a good thing by admitting to the steal - he didn't try and lie about it, and that is a positive thing. I agree with the other posters who say there's more going on behind this, and just heaping on punishment after punishment won't solve that.
His punishment is : Having to pay the money back with chores (no matter how slow or how much ill grace) and knowing how hurt and disappointed you are.
In my view, that's enough. I'd let him go on the trip. Perhaps without spending money, or with less than others.
Are you finding things difficult financially in ways he's picking up on? at 8 I imagine he's doing a lot of comparing with peers. Maybe he feels hard-done-by. And if so, that's something he's going to have to come to terms with.
Whatever you do or don't decide to do, please keep reassuring him that you love him, but you hate the bad choices he chose to make.
Also, we tend to say that "the behaviour you give attention to is the behaviour you get", so please try and find some positives to praise and verbally praise them, and I would hope you'd get more of that.
Good luck 