You can download the standard Tayasui Sketches at no cost. It includes basic tools like the pen, felt pen, and eraser.
This is typically an in-app purchase or a separate "Pro" bundle. Prices vary by region but generally range from $10 to $20 USD for a one-time Pro upgrade. Key Pro Features Upgrading to Pro unlocks the app's full creative potential: Tayasui Sketches
You should only download the app through the Official Mac App Store to ensure you are getting a secure, virus-free version.