CDs work, but they're a big pain the backside (slow, lots of swapping discs, bad burns), and they're not as permanent as many people thing - the media degrades and is often un-readable after a year or three.
I don't know enough to suggest what alternative would fit your requirements / budget. Whatever you choose, regularly check that you can restore files! Make it a weekly, or monthly test.
More than once in my career I've encountered huge, elaborate and very expensive backup schemes which do all sorts of fancy stuff (using robotic tape changers and all sorts of funky tech), but ended up having a conversation like this:
me: Hello Mr. friendly sysop. We found a file which was corrupted a few days ago, and we were hoping there is a backup from the 15th. Do you know if there is one?
sysop: sure, we should have incremementals for the last two weeks.
me: Oh great, this could really save us a lot of pain! Can you restore the file from the 15th please?
me: What do you mean by "ah"?
sysop: Well, we have backups... it's just that our restore procedure doesn't work.
I kid you not.