If you're looking to get your parents to say yes to something that's going to cost them money, one way to sweeten the deal is by offering to pay for part of it yourself, or doing extra chores around the house to earn money to contribute. This shows that you're serious about wanting what you're asking for and are willing to put in the effort to make it happen. Plus, it can help offset the cost for your parents which makes them more likely to be on board.