There would be no way I would be giving my grandson either the money or paying that sort of price for any present. Even if I was a millionaire I would not want to be spending such amounts on a child of 12. He is obviously learning from his parents that he can ask for ridiculous amounts and expect to receive them. You would not be doing him any favours by letting him think that other people provide what you want and you make no effort to save or find ways of working to get something he wanted. That he needs to learn to think what might be possible and also learn to choose from things and not think that he is entitled to whatever he wants. No one can expect that , whoever the might be even Donald Trump. !!
So I feel that you need to sit and think about things and how you want things to move along. So do you have any real contact personally with him? Do you share any interests, such as chess or football or any particular thing, where you could find something like a book that was connected with the interest, or a possible ticket to visit some exhibition or watch some game. I would hope that you might be able to have the opportunity to have some personal contact with him as he gets older, and that he will then begin to understand that you are not just a money bank but a person with ideas and thoughts of your own and might begin to be interested in you as a person,
One problem is the adverts that always annoy me by saying something is "only" whatever price, implying it is not much. When my son was small and asked for something that was very expensive, I told him that he could not have it, but could see that he didnt really understand what the amount of money represented. So that day, I laid out on the table food for all the meals for a week for the three of us. When he came in I explained that if he had the money for this toy, all three of us would have to go without any food for 6-1/2 days. He looked a bit shaken and I went through it again and we looked at the various foods and I asked him whether he would mind not eating this or that etc. It did sink in and he was able to understand much better. As he grew older I was able to refer back to that occasion and ask if he thought it was fair! He did not always like it but did realize what the actual amounts of money meant. I think that it is sad but probably true that at some point you have to say no, and see how he reacts to this. If you allow this to happen you are encouraging him to leech off other people, think that money is the be all and end all, and that he does not need to empathise with others or understand the world needs give and take. So by giving him this money , I think you will be just putting off the inevitable. Perhaps you could put an amount that you thing is reasonable, in an account, still in your name , not his, and then you have the rights over the account. Then you can add to this, without him necessarily knowing about it. Then if things improved over the years you may have a relationshipin the future where you could then give him this money and explain that this was saved for him over the years, so that he will know that you thought of him even if he did not know at the time. Do hope he grows up to have a better attitude to life, and that you dont let yourself be pushed into giving something you cannot afford and also do not think it is a good thing to do. I much prefer giving special occasions to grandchildren , so that they might have the first chance to see a ballet or go iceskating or something a bit unexpected. They do remember doing things more than having things, in my opinion.