Reasonable gift for not attending a wedding

[Thinkcalmthoughts]

My future hubby doesnt get on with his brother and haven't spoken in years.
Months ago his brother moved up north so technically hes not far say a hr or so (were in Scotland too)
My hubby to be's mum did say to us a while ago that we were invited to his Bros wedding in December but we never received a invite so as there was no invite and no one had remind us we forgot the date but knew it was in December at some point. Saturday there his mum turns up st the house with a invite to the wedding a week before (weddings this sat ) at that point I said we cant as we have plans and it's my mums birthday the sun theres a table booked for a birthday dinner with the family including my 90 year old gran.
Let's say his mum was less than impressed but who gives a invite to a wedding a week before the date that would be like us doing that for ours next year

Anyway I said to keep the peace that we would buy a card and a gift to say congratulations on your wedding day as I wasnt cancelling plans for a wedding where I've never met his bro or future wife

As we are watching the penny's just now what with mums birthday this weekend his boys birthday the weekend after xmas then my daughters 16th in jan plus saving for the wedding and still to get some stuff done for that as well as save for a house we were thinking as a wedding gift a voucher and some nice champagne flutes plus a card is this reasonable?
As surely a gift of any kind is acceptable and its the thought that counts

[gamerchick]

I'd just get a card.

[Thinkcalmthoughts]

My partner had said to his mum he was getting a voucher and something else she went how much is voucher he replied £10 she told him that was rubbish.
Ehhh there getting a voucher champagne flutes and a card how much is she thinking we can afford especially seeing as got the invite last min can safely say he or we are not in the good books with his mum oops