What Do *You* Want?
Is that a hard question?
One would think this is the ideal situation for someone to be in. You get the opportunity to say "this is what I want" and let the other person can decide if that sounds appropriate to the situation or not.
Many times it has come to this - the "what do you want" and "what do I get" discussion, and it winds up being a royal pain in the ass, in my experience. Why? You obviously know what the top demand will be - sexual pleasure, but perhaps it's actually less. But the other party doesn't know what you're looking for exactly. It could be a variety of things - money, travel, a place to live, shopping sprees, who knows?
Be assertive, be direct, be honest. You'll get what you want, or you'll discover you're wasting everyone's time including your own.