What generally impacts the cost of professional drain cleaning?

I recently had a frustrating experience with a slow-draining shower that eventually led to a backup. While I managed to clear it myself, it made me wonder about situations where professional help is unavoidable. I’ve heard stories about drain cleaning costs varying wildly, and it’s a bit confusing. What generally impacts the cost of professional drain cleaning? Are there specific factors like the type of blockage, location (indoor vs. outdoor), or the tools required that really drive the price up or down? I’m trying to get a clearer picture for future reference.