What does a derailleur do on a bike? How much does it cost to replace a rear derailleur?

What does a derailleur do on a bike? How much does it cost to replace a rear derailleur?

#BicycleGearsAyoub Rhejjou
A derailleur is a mechanism that is used to move the chain from one gear to another on a bike. It is typically located at the rear of the bike a...