But this bloke devised a Vocoder using THAT ICs which are accessible but not cheap, however you'll need 39 of them (!!!) and the panel/board set alone is going to run you another $250 plus shipping. If you look at each of the filter boards, you'll notice that they are PACKED with parts, so not an easy built but a very nice one.
He has some samples and pics here: http://l-1.su/Vocoder.html not to mention some pretty convincing samples speaking Russian ala Kraftwerk "The Robots"
