Heres what i would do , Back up all the important info onto an external hdd once every month and store this offsite , such as a friend or realitives house or even the bank if needs be
And have another external HDD you jhave cpnnected to the pc all the time which you back up onto at least once every week , that way the most you will ever loose is a months data
I wouldnt say DVD's for the fact that it wil get costly in the end and also it takes time to burn that many DVD's
There are also backup programs which will only copy accross stuff wihch you have added since the last back up
I would dismiss online storage for them volumes of data right away as the time taken to both upload and in the event of it being required download that data could take a while so not realy a good choice