The words describe different aspects of ministry rather than three fixed ranks.
A preacher is anyone proclaiming or explaining God’s word… A pastor is someone entrusted with shepherding a particular congregation (see this thread).
A priest is different. You usually run into it in churches where ordained ministers serve at the altar and administer the sacraments.
So one person might be all of these at once, ordained as a priest and serving as pastor of a parish, while also preaching during worship.