Yes, an IDE drive will work.
For example, I found an old 1 GB IDE drive in an old computer at work. It served as an intermediate upgrade. But then I took the old 80GB laptop IDE drive from my Mac Mini G4 with an adapter to the full size IDE and it works well too. Way too much space for the 5200CD, but pretty sweet.
Technically, you could use an IDE SSD if you wanted, but it's kind of a waste.
Just look on eBay for IDE drives. 3.5" work without any fuss. You should be able to find something for super cheap. Alternately, look around local computer shops or e-recyclers for options. Or just ask friends if they have any old computers lying around that might have an IDE drive in them.