How to commit to saving up for something?

So I want to save up for a pair of Beats Solo 2 and it'll take me up to 18th December to save up for then, how do I commit to this? I'd ask my mom to buy them for me but she's already getting my iPhone 6 screen repaired for £70 and I don't want to make her spend £99 on this pair of Beats. I've already £11 so I need to save up £88, how do I commit to this?

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