No, there is no monthly fee for the Fire Stick. However, Fire Stick does require a one-time purchase price of $39.99 (USD) or $49.99 (CAD) for the device.
Once you've purchased the device, there is no additional cost required to use it. However, you will need a subscription to certain services, such as Amazon Prime Video, to watch certain content. Amazon Prime Video requires a monthly fee of $12.99 (USD) or $7.99 (CAD) per month, after a free 7-day introductory trial.
You can also purchase or rent individual TV shows or movies from an Amazon Prime Video subscription. Prices will vary, but you can find more information about pricing and rental terms here:
https://www.amazon.com/gp/help/customer/display.html?nodeId=GDMFFW6J8T6TQ2QT.
If you're looking for a more comprehensive streaming service that includes access to more content, you may want to research other services, such as Netflix or Hulu. Both offer a variety of plans with different subscription fees.
Overall, the Fire Stick itself does not require a monthly fee, but you will need to purchase the device and perhaps a streaming service in order to access and watch content.