I've got two extra PlayStation to GameCube Adaptors
They are imported from Hong Kong and work great. They even support the rumble feature.
One is new in the plastic package, the other was opened only to test them. I've enought controllers so I don' t need them. I was mostly just curious.
$25 for the Pair, $30 shipped in the US. They were originally $15 each from HK so the shipping alone would have killed!