Seeing as your image link doesn't work I can't see exactly what you're wanting to back up, but there are 3 plausible options that don't involve CDR.
If you want to back up whole drives, you can allways image them to another drive or drives. Most imaging programs (such as Norton Ghost) offer image compression which may or may not prove to be much of a saving depending on what you're backing up. For example, if you're backing up lots of text based stuff (website source, essays, financial info like spreadsheets and databases) you can expect a good compression result. MP3s or DivXs will not be compressed much if at all.
(2) Network storage:
If you have another computer available to you on the network then you could back stuff up to drives on it.
(3) A combination of 1 and 2.
There is no cheap way to back up large ammounts of data, so whatever you do it's going to cost you.