Plastic’s and silicone are the most common materials used for keyboard covers on Macbooks and Macbook pros and indeed most laptops. Some covers are made of a faux leather material but this is more to protect the actual laptop screen than the keyboard.
What would be the main Reasons that you should use a keyboard cover on you Macbook pro or Macbook computer?
Answer because you want to take care against undue wear on your computer -if you are using the keyboard then it does wear the keys eventually. Especially if you use the laptop a lot then you would want to invest in good protection for it, an external case is often another common investment people make.
You might want to prevent dust and fluids damaging the keyboard or worse the inside/internals of your laptop, and using a cover is going to make sure that you have that protection.
Where can I find keyboard covers for my Macbook pro 13″ / 15″ / 17″
The apple store stocks the more expensive types, for budget go to eBay and put search criteria too world wide to find the el cheapo ones from china and hong kong. You will however notice a difference in quality and niceness to use!
What sort of likely investment cost am I looking at.
Anywhere from roughly $1 to $40 though I personally think $15 will buy you a cover that is good quality and fits snugly on the keyboard without blowing your budget too much (there are so many other things to spend your cash on!)