teen with deadly brain tumour has almost raised $ 80,000 .
the money is needed to fund his life-saving brain surgery .
18-year-old jackson byrnes has stage four brain tumour .
he was told by doctors it was too aggressive to operate on .
instead he found a neurosurgeon who would do the operation .
he must find $ 80,000 by tuesday night to pay the surgeon up front .
jackson byrnes and his family have used crowd funding to raise money .