First thing is, it's the only thing he's put on his list, it's not a random item amongst some other stuff. So that suggests it's particularly important to him and he's football mad, so he's probably going to have scrutinised it in detail.
Here's what I'd do... I'd have a conversation with him about it. Explain that a ball at that price is a collector's piece rather than for a daily kick about. Be honest with him. Tell him if he really wants THAT specific ball at that price, then it's something to display and keep rather than play with. Don't say it's not worth getting because he's a kid and because he'll lose it or that he's not "grown up" enough to have it. He'll just hear that HE isn't worth it. Explain that it would be horrible for him to get such a special ball and for someone else to steal it or damage it - invite him to think about what that would feel like. Then suggest either a more affordable alternative replica that he can take out and enjoy playing with, or he gets the expensive one but it's not for playing with - possibly he also gets a cheap normal one for playing with - and also point out that he won't get much else. Present the options to him so he can make an informed decision. Suggest he goes off and thinks about it. If nothing else it demonstrates the process of thinking through things carefully and weighing up pros and cons. He's only 7 but it's never a wasted exercise.
I see no harm in having that conversation with him - it manages his expectations and he gets to consider alternative options. It's also better than attempting to pass off a replica or cheap knock-off as the real deal. My parents always did this and while I never complained because I wouldn't have dared - I always knew. I hate this attitude that kids won't know the difference - they really do - especially when it's something important to them.
Talk to him - explain - give him the choice. Of course it's up to you then to hold him to the choice he makes. If he goes for the expensive ball then he accepts it's not leaving the house so may have limited enjoyment of it. People will say he's only 7 - and he is - but it's clearly important to him and his reality is that he's dreaming of getting that ball on Christmas Day. There is nothing to be lost in having a chat with him. You can then make the ultimate decision but don't just assume what he's thinking - give him a chance to say what he thinks.