Modest, inexpensive, formal dress help please.

[TickledOnion]

My lovely mum needs your help.

She's going to a very religious Jewish wedding so needs a modest (high neck, mid to long sleeve, long length), formal, not too clingy dress.

She's 68 years old, 5ft4, size 12-14.
She suits strong dark colours, nothing muted or pastelly please.
And she doesn't want to spend much as she won't get much use out of it. So less than £100 ideally.

Please help. Thank you.