Someone please HELP FIND CHEAP flight for august (MANCHESTER TO TENERIFE SOUTH)?

ok so me and my mum use to go on holiday with our grandparents, however due to their age and medical conditions they are no longer available to fly, therefore me and my mum have not been on holiday for several years. I have found the complex in tenerife that we use to go to twice a year with our grandparents anyway... show more ok so me and my mum use to go on holiday with our grandparents, however due to their age and medical conditions they are no longer available to fly, therefore me and my mum have not been on holiday for several years. I have found the complex in tenerife that we use to go to twice a year with our grandparents anyway by some flicker of amazement (they have got a week in august the same week me and my mum are off work, and they have offered it us, this place is mainly owners and EXTREMELY hard to get in) HOWEVER, we have 3 days to leave a deposit, the only problem is i have checked ryan air, jet2, johnson, easy jet, ba (the usual cheapest flights) and they are all wanting around £1,100 for return flights, going there is a lot cheaper than coming back the dates are 23rd AUGUST - 30TH AUGUST 2013 i can find flights for around 200 going there but coming back they are around 700 (the cheapest) there is only 3 of us (2 adults, 1 child the child is 7) we wanted to pay around £500 tops as the complex is not all inclusive it is self board so we have to think of spending money ideally we would like to pay around 400 pounds, does anyone know of any uncommon airlines that are cheap however reliable? or could anyone find a price for a flight at that price? PLEASE HELP only 2 days left on our childhood complex :( that my brother has never seen or been on an aeroplane
Update: i have traveled PLENTY of times and know it is the PEAK season ... the question is not WHY are they expensive it's WHAT ARE Unknown cheap flights, also.. seen as its peak the 23rd is very cheap on most flights
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