My ex-boyfriend asked me to travel.

Since you call him an ex-boyfriend, it means that you have a current boyfriend now. In your present situation, unless you want to get back together with your boyfriend or have other ideas, you'd better not take part in this activity. Otherwise, it will bring you some troubles, such as your relationship with your current boyfriend. Even if the problem is not big, it will interfere with your normal mood. As for your ex-boyfriend's idea, why did you choose such a special place when he was free? Besides, neither boys nor girls care about the price, at least on the surface. So I think he has an idea. If I were him, I would find a reason to ask you out, lest you refuse directly. It is more feasible to find a few people to go with.