If you are just trying to make tones, a handful of transistors, inductors, capactors and resistors will do. True, the circuitry may not be adaptable to what you plan to build in the future, but it would show some fundemental aspects of electronics. It can be a little tricky, to build the tone generators.
In any case I have also made audio tones on a microprocessor.
Each tone generator would consist of one transistor, 2 resistors, `one inductor, and four capacitors. About that, I don't care to come up with the exact numbers. Sometimes, theres trouble building it right, but you can find the operational point in one day. But sometimes it would only take 30 minutes. I recomend that you make about 5 or so audio tone generators for future use. House, them in metal or plastic boxes.