It's not about money, but about specialness and thoughtfulness.
I suspect that a bargain dinner and a plastic badge display none of the specialness that make marking birthdays (or xmas etc) well, special.
If the restaurant was one that meant something to the both of them, then the cost is irrelevant. Likewise the vw badge.
But I suspect that's not the case?
If it helps at all, I'm with you on the sadness that comes with seeing the other parent disappoint your child just at the moments where they should be happy.
It feels extra cruel because people of any age are so vulnerable at moments of celebration. It feels even worse than an everyday let down, if their parent can't even get it together just for one day, or one evening.
My stbxh turned up Christmas Day evening (after having promised DS he'd be there in the morning), with a child's tablet. DS went to bed very happy. And woke up on Boxing Day not being able to find the present, which had strangely disappeared, along with his father.
Turns out the sodding bastard took the present back to respond the money on himself. Wanker.
I don't know if DS remembers it. I hope not, but honestly, it's the kind of thing that sticks in your memory somewhat.
What kind of father does that?