God bless you, KAC. I strongly recommend you talk to your priest, and maybe contact your diocese and ask to talk to a vocation director. You may also want to find a religious community (monastery, friary, etc) and talk to a religious.
What you learn in seminary depends to some extent what seminary you go to and what type of ministry you’ll do. But generally they teach dogmatic theology (faith), moral theology (morals), Scripture, how to preach, and how to be a shepherd, among other things.
Formation time and cost depends on what kind of ministry you’re going to do. Generally speaking, the shortest formation I know of is about 7 years; the longest about 15 years.
Cost also depends on what you’re doing, and is generally comparable to the cost of attending a university. Many dioceses and communities cover the cost of formation as long as you stick with it. Don’t let that be a source of anxiety; if you are called, God will provide.
There are two main kinds of priestly ministry: secular and religious. Secular or diocesan is what your “regular” parish priest is, usually pastoring a parish somewhere. Religious means you also take vows (usually poverty, chastity, and obedience) and live in community. Secular priests make a promise of obedience to the bishop and in the Roman rite live celibate (with a few exceptions), but they don’t take a vow of poverty. (A promise is made to a person before God; a vow is made directly to God.)
Of religious there are two kinds: contemplative and active. Contemplative means more separate from the world, like in a monastery, such as Benedictines, Cistercians, Carthusians, etc. Active means having more contact with the local community, e.g. teaching or working with the poor, such as Franciscans, Dominicans, Jesuits, etc.
It would be a good idea to investigate one or more of these options, speak with a vocation director and see what it’s about.