Too often, this is simply the wrong question.
People will almost always ask it when joining a gym or in entering a relationship with an exercise professional.
Money matters and cost awareness is a good thing. And, of course, budgets have to be considered in such a transaction.
However, when that question is posed first, it is a smoke screen.
Perhaps the following question ought to be considered first: "What am I looking to buy or get out of this venture into exercise?"
Real help for my physical health goals? Status? A friend / enter-trainer / dime store therapist? External motivation?
These roles all have different monetary values. Once you know your answer, then you can accurately consider your budget. You can also consider why you want what you want, meditate on it for a while and, potentially, reconsider your drive to purchase in the first place.
Because no genuine exercise professional wants to be anything other than just that in his or her relationship with you, and that is something worth your top dollar.
In my experience, that is the process wherein most prospective clients find the greatest value.