WANTED: tone generator 20hz to 22khz sinewave

Hi there all
All i want is the following and im having a hard time finding it..not sure why...
A tone generator,
basically, selectable SINE,SQUARE,SAWTOOTH WAVE
it must have selectable (pot) frequency between 20hz to 22khz

sinewave is a must have.. saw and square a bonus.

its simply a device i want in order to work on my amps. i.e inject signal X into amp, check output...

where can i buy? cant see how something like this should cost more than 300 - 600rand...

any ideas?

regards
Anton