(As long as you can afford it) Just spend what you need to get him what he wants/will make him happy/excited. There doesn't need to be a target.
Some years he will want cheap things.. no need to force yourself to buy more.
Some years he will want things that are over budget, and I wouldn't arbitarily say no, unless I couldn't afford it.
E.g.
at 2 my Christmas was really cheap because my son was into cars, and it doesn't cost a lot to impress a little boy with new car toys.
at 3, it was a lot more expensive because he was after playmobile and Pokémon, neither are cheap where I live, because they are both imported...
But at 4, it was back to cheap, because it just happens that the toys he is obsessed with are not at all expensive, so he can have quite a few for very little money.
Then later, I'm sure it will go up, for the years that he wants tech presents etc. And down if there is nothing big he wants..