How to convince my dad...?

How can I convince my dad to buy me Lego.You guys might think I am weird a 14 year old that play's with Lego. I live in Saint John Canada and on the Zellers flyer, I saw Lego on sale, Buy one reduced set, get it 30% off. I want it because I really need it for my stop motion movies and I really want it. My dad says no because he thinks he has to pay for it and I have money in my bank account but he says no. He also says I have alot when I don't.