Buses from the airport to Torrevieja run every 2 hours from 10.00 to 20.00 and return ticket is about €13/14 per person and the journey is about an hour. From Torrevieja you can then take a bus to Guardamar. In all honesty it would be a big faff with a potential 2 hour wait at the airport if you just miss a bus. If you want to go by bus take the bus into Alicante and change at the bus station and take the Torrevieja bus and get off at Guardamar and walk.

Alternatively take a taxi, 20 minutes journey time and about €45 each way and door to door.

Thanks for that
as I have plenty of time....I will go via alicante