Sounds like the teenage blues !!!!!!!!! but I know what you mean . Children now expect everything to be handed to them but you are right not to give in to every whim . Its blackmail really . they make you feel like a bad mother. They dont understand or care that your hubbie and yourself work hard for your money. I would set them various chores to do for the next few weeks like mow the lawn, empty the dishwasher, help folding laundry , pair the socks (hate doing that) and then say you will concider their requests. 1: it might shut them up altogether or2: you might get them to realise they have to work for what they want. (I sound sooo like my mother !!!!)
I am lucky here in that my eldest (17) with autism is happy with a box of crayons or some paints and the 15 yr old in fairness to him is not too demanding either . If we tell him we dont have the money at the moment or its too expensive. he is usually ok with that.