right now its sort of vague, its really in the early idea stage. In the picture above i have a max 038 IC but i realized this wouldn't be optimal, my understanding is that the IC isn't really for producing varying frequencies, its more for using components to get one frequency out and thats it. Not to mention its not manufactured anymore.
But to answer your question, the idea i have in mind should be fairly cheap, since its in my head i can only give a rough estimate (and assuming the design in my head works) it should be very cheap. The most expensive thing that comes to mind is the atmel processor for the ardunio uno, and the op amps.
Thanks for your interest, and any more questions or help just let me know!