Were can i buy a cheap guitar?

i really want a acoutic guitar for xmas becaues my skwl does free music lessons, but i asked my mum if she can buy me 1 and well her answer had a lot of swearwords. ive been asking her for a guitar every xmas for the past 5 years and i looked on some music shop websites and a good 1 cost like 150 quid. and it will take me til im 18 too save up that much. so were can i get a cheap guitar that is still a good kind and my mum mite actully maybe buy?