If you already own a shiny Rayquaza in your collection, it will cost 20,000 stardust and can be traded to you in 24 hours.

Unregistered Shiny Trade 

If you do not have this shiny Pokémon in any form, it will cost 1 million stardust if you want to trade now. There is a second option where we can add each other as friends and exchange gifts for the next 30 days until we become Ultra friends. When we become Ultra friends, it will only cost 80,000 stardust.

Have a great day!