There are some monochrome thermal printers around which are quite cheap, and print on plain CD-Rs.

I think Casio do one... yes - Amazon have them listed... the only way AFAIK to do colour is to change the cartridge (or have more than one with different colours). Methinks registration for multiple colours would probably be unreliable, and photographs would be out of the question.

If you just want fairly simple text labelling for archiving, such a printer would do the job efficiently and cheaply.