to my knowledge, abu never made a c4 spinning reel. if you're talking about the old ambassadeurs with non-palming side plates(flat left plate with a brake knob in the center), they're pretty collectable. some were made in rare colors like a brown 5500c, others are just out of the ordinary nowadays, like the 5000D knucklebuster
the price ranges from 30-150$ usually on those kind of reels, depending on what shape theyre in. i know quite a few people who still use them, since they're very durable and handle big fish very well
abu still makes reels that look just like the old ones, only thing is that they're not usually sold in the us. some popular models are the 6500CS rocket, 65/5500CS Mag, and 6500/5500C3CT
one of the main reasons i use abu's reels is because they use brass or stainless gears in all their reels. shimano and most other manufacturers besides maybe penn use nylon and plastic gears in their reels. when you use them in cold weather with big fish, they tend to break. that, and the cost of fixing an ambassadeur is far cheaper than say, a calcutta. just keep it oiled and you probably won't even get that far
[edit] i didn't check the link. never thought an old cardinal could fetch so much on ebay, i've used them for years and they're good, but not the greatest spinning reels out there