I have seen it in certain instances. Sometimes it’s an “independent” lay spiritual director, where that is part of their livelihood. In other instances it is a spiritual director attached to a retreat center that takes “suggested donations”. That being said, not all spiritual directors require a fee. When I started formation to the diaconate I asked my pastor if he knew of any local priests that offered spiritual direction. After he gave me a list of names, I spoke to a handful of local priests and was able to find one that was available. When I asked if there was any costs, he looked at me kinda funny and said “no, part of the role of a priest is to help people discern where God is leading them”. He said I was free to toss extra money in the collection if I felt moved to do so, but the diocese already paid him.
Personally, I am a little leery of spiritual directors that are “paid professionals”. That is doubly so for those that have a fixed fee. For many people a $50 fee each month could be 2 - 3 hours of their own after tax wages. I don’t think our financial situation should be a barrier to strengthening our relationship with God. I guess there is a part of me that feels turning spiritual direction into a business leans too much towards the thoughts behind simony.