Depending on the age/model of the Philips there may be a way around having to buy the dearer audio disks.
The early Philips models allow the user to put in an audio CD-R, initialize the CD, and then pry open the CD tray and swap it for a cheap data CD, and then record on it.
Philips caught on to this and, from the 765 onwards, their recorders are designed to prevent it and there is, alas, no other work around.