Get her a 40th birthday card (with badge) just for the chuckles.
Always enjoyed the all you can eat chinese in glasow opposite where hsbc used to be. Prolly not posh enough for what you are after tho.
A lot of women don't like age jokes. Pic please...
Unless she is the type that is bothered about money then I wouldn't worry about spending 'enough'. For most women it's the thought that counts, that you have bought something with her mind mind that means something.
But I wouldn't suggest breaking the bank either. Try and think of a gift that is personal to her/you both and you'll be on a winner 
