can i purchase airasia ticket from nanning to klia2. what is the cost range n where can i purchase?

Yes, of course you can purchase the ticket.
The fare cannot be estimated exactly because it changes frequently. It costs around CNY 1,500 for the single trip these days.
About the ticket booking, you can ask help for TravelChinaGuide. They provide this service with high efficiency. If interested, their contact information is bookingtravelchinaguide.com.