How can I convince my mum to let me buy these shoes?

I have been wanting a pair of Nike dunks I see at the store for ages now...and I have enough pocket money to buy it-- but it's pretty expensive and my mum doesn't let me buy them because she thinks its a waste.

I have a pair of classic Converse, and I want a pair of Nike dunks. How can I convince my mum to let me buy them (with my own money)?
Let her know that you will learn how to spend money on something useful instead of a waste, in a few years, when you live on your own.
"Mum, it's my money and I'd like to use it on this please. If I don't like them, then it's completely my fault and I have to live with it"
Tag: How can I convince my mum to let me buy these shoes?