MacBook Air 2014 motherboard price please

Contact your nearest Apple Store, or Apple Authorized Service Center for a quote. This is a user-to-user support community, and other than the Apple staff that manage and support the hosting activies of these communities — Apple is not here.

Apple doesn't sell you parts. You'll have to take your Mac in for them to replace it for you. If you plan to replace it yourself you'll have to look at other places.