Is 1400pounds for a high performance laptop preposterous,how to convince my parents to buy it for me?

i want a macbook pro that will meet my gaming requirements for a minimum short term perspective of 3years to come. I am very keen in these games GTA4 and mercenaries 2.Both of these games requires high performance hardware to get the best gaming experience. I recently brought GTA4 and running on the minimum requirements on my desktop was awful. The gaming experience was totally tainted by my clumsy computer which is 2 years old now. the macbook pro which i fancy after customizing was about 1400 pounds. I felt totally compelled at 1st to raise the request t my parents. when i said trying to be optimistic about 1500pounds for my dream laptop they were stunned and began haranguing about how ignorant and absurd i am. am i really asking for too much for a birthday if not i am willing to sacriface my xmas presents and bdae presents just for this laptop.My dad brought a laptop for 700pounds..... my mum said, i really want this laptop. why do all the teenagers get to play the awesome games? how can i convince them? and if theres any chances the british currency strengthens my chances are improved... any suggestions?