They are not very rare... I picked up a boxed C64 speech synthesizer CIB for $12.53 on eBay 6 months back. You see them pop up every few weeks and they routineley go for between $8-40 depending on how many people are bidding at the time. The highest I ever saw one go for was $65 in a buy-it-now... the buyer must have been on crack to pay that much.
