You do not need a lot of money to have access to square, triangle or sine waves in the audio range.  This simple kit uses four operational amplifiers (op-amps) to deliver these waveforms in the 6 Hz to 7000 Hz range. 

The sine wave is a pseudo sine wave produced by a very simple wave shaping circuit.

The kit is constructed on a single-sided printed circuit board (PCB).

A pseudo or imitation sine wave is produced by a wave shaping circuit.  A diode is a non-linear device.  As the potential difference across it increases the current rises in the characteristic way published in all textbooks.  This circuit "joins together" this characteristic curve to produce an approximation to a sine wave.  two diodes have been joined together as a series pair in order to provide a higher amplitude than would be obtained using only a single diode.

The shape of the pseudo sine wave could be improved at any particular frequency by filtering, but filtering will cause distortion at lower frequencies and loss of amplitude at higher frequencies.  You can have perfect sine waves at particular frequencies by switching in appropriate filters at those frequencies.

The sine wave is sensitive to loading and must be buffered.  It is also low in amplitude and needs amplification.  R9 & R10 set the gain of op-amp B by forming a voltage divider between the source and the output.  If the wave shaper voltage is 1 volt higher than the reference (at the non-inverting input) the op-amp reduces the output voltage until the inverting input voltage set by the divider is equal to the non-inverting voltage.  The ratio of the values of R10 to R9 give the gain.  The gain here is about 2.

Operates on 9vDC.