I think you are being quite unreasonable, yes. The money is largely irrelevant. Supposing you had chosen first, but your choice was only £10. Would your husband then be forced to match your gift's value when choosing his own?
It's the gift that is important, not how much is spent on someone.
I used to work with a girl who had twins. I think they were about 2 years old. She told me that she'd been to buy them slippers and one boy's slippers were (for argument's sake - this was 20odd years ago!) £8 and the other boy's were £7. She had to buy the second boy something for £1, just so she had spent the same on both of them.
For me, that would just mean that one child had two gifts and the other just had one.
Diff'rent strokes for diff'ren folks, I guess.
For me, I don't care how little a gift costs. It's as long as there has been thought behind it.