Are we talking CDs or DVDs? BIG difference. But even CDs, that's a lot of files. What are you backing up? If you're backing up the entire PC (not recommended) then it will take a lot. And if these disks are Write only, you're gonna spend a lot in disks.
Best to only back up what you can't afford to loose such as pictures, music, documents, etc. The rest can be restored with the factory discs.
What I prefer is an external hard drive or internal slave. Takes a tenth of the time and I back up only what I don't want to loose. Yes, hard drives crash. But the chances of both drives crashing at the same time are minimal. I actually back up my web site to an internal slave drive and to DVD-RW. And once a month or so I clone my drives to yet other external drives. I do not use backup software. I've seen too many horror stories of the backup being corrupt, having to install the backup software again, etc.
Windows is a resource hog. Make sure the PC is up to snuff before you attempt it. Go to the Microsoft W7 tool and test it first.