Is there a way to purchase Airplay for my macbook pro computer?

You need 10.7.5 or later and a MBP that is Airplay cabable. The list of Airplay Macs is:

• iMac (Mid 2011 or newer)
• Mac mini (Mid 2011 or newer)
• MacBook Air (Mid 2011 or newer)
• MacBook Pro (Early 2011 or newer)
• Mac Pro (Late 2013)

If you don't have a 2011 or newer then you're out of luck.

airplay mirror rely on the video card of the computer supporting realtime encoding of the image to a H.264 stream to transport over the network to the appletv

if the video card does not support that feature and older ones does not then the main cpu have to do it which will mean worse performance of both mac and what is seen on the tv

the program called airparrot is a way you can pay for the feature it rely on cpu encoding so it can cause a bad performance