Practically, the only difference between a ceremonial athame and a kitchen knife is that an athame has a double-edged, leaf-shaped blade, whereas a kitchen knife has a single-edged, stiletto blade. The only function of an athame is symbolic. Its symbolic significance is the one that you, the user, ascribe to it. So if you are convinced you need something that looks impressive, then you might struggle to invest a kitchen knife with equivalent symbolic power. For me, the power of the symbol is not something inherent in its unique shape and function, it is just a metaphor. The knife is a metaphor for the fertilising principle, and as I'm solitary, no-one else is going to look down on my moneysaving alternative, so the fact my athame is really a kitchen knife makes no odds!