Here are my suggestions for the mother of the bride's outfit.
The groom's mother can also use some of this suggestions, but do check with the bride about wearing light colours. It is quite nice when all the wedding party wears light coloured dresses, but when it's just the bride and the mother of the groom it somehow seems weird... someone might think you want to steal the show.
I have to say I wasn't inspired by more affordable fashion. But I'll keep looking and might update this page as I find more solutions. My preferred options is the Biyan dress over trousers followed by Gianbattista Valli..
|Erdem - Net a Porter £2380|
|Gianbattista Valli Couture - Matches Fashion|
Roksanda Ilincic Sessler color-block pleated silk-crepe dress
£1,270 on Net a Porter
|Biyan £1610 - Printed silk dress on Net a Porter|
|Victoria Beckham - £1800 on Net a Porter|
|Emilio Pucci £ 920 on Net a Porter|