It retails for $585.00 from Marni.com
Or you could try these similar looks for less:
From the outnet.com by Tibi for £99.50
From House of Fraser for £64.00
From Farfetch.com by Marc by Marc Jacobs for £184.00
And this one which is my favourite from Dorothy Perkins for just £30.00
It turns out this is a really hard dress to match due to it's light pink flowers.