first, if you are in charge of some aspect of planning such a retreat, or have questions about the requirement for a candidate in your care, find out what is required in your diocese.
In this diocese an overnight retreat is supposed to be a requirement for confirmation, but there is a severe shortage of acceptable overnight facilities that meet safe environment guidelines (and in our parish, a shortage of adult chaperones). an alternative is something like Youth2000 this weekend, which is 3 days, but kids do not sleep overnite, returning to their own homes each evening.
typically a retreat such as this is planned by whoever is in charge of coordinating the confirmation program, and they may hire presenters, invite presenters from elsewhere in the diocese who are not paid, but get a stipend, or have catechists or other suitable parishioners give presentations. The content should focus on the sacrament itself, the duties of adult Catholics, discipleship, the Holy Spirit, gifts of the Spirit or some other aspect related to the sacrament.
Cost should be reasonable and based on actual cost of facility, room, board, materials, presentations, transportation etc. It is reasonable to expect the parents to pay all or most of the cost, but the parish to subsidize those who genuinely cannot pay. I forgot the rest of the question.
as a practical matter, since I have been here, I network with other parishes and the diocesan offices, and so our candidates are offered several choices of retreat experiences that “count” for confirmation. Our parish “Spirit Day” is the Sunday before Confirmation and is an all day, intensive period of quiet prayer and meditation, punctuated by some brief, pointed presentations focusing on the Holy Spirit. Parents provide light meals, and I will give presentations at other parishes, while their catechists or DREs will return the favor and presen here. We try to invite priests as presenters, but that is iffy, it is even hard to get 2-3 priests to come and hear confessions.