Lol that is an extremely cool retro recording.

God bless cassettes, and the folks who have held on to them. I don't know why, but for some reason when I was growing up Casios always had a bad press from me and my keyboard chums. We all seems to go for yamaha or one of the supposed cooler makes. Maybe it was some kind of fassion thing, if keyboards can be subjected to the fickle laws of fassion.
But I have no idea why it should be worth so much, unless it's just a retro thing. Probably.
I saw a shagged out bontempi type organ in a club I was at the other day and wondered idley about buying it. I decided not to in the end as it was full of dust and I have enough crap in my house as it is. But I looked on ebay to get a price idea and had to chuckle at some of the asking prices for similar models.

These will be the stuff of antique shops yet to come.
Back to Casio though.
Nothing to do with your question, but on my track Tigers in the Butter, I wanted to use a sound from an eightys casio one of my friends had. It was a kids keyboard really, but it had a couple of beats and sounds.
I had a 20 year old cassette containing a recording of it, done by a pretty crappy tape recorder, but the level was good and there was a clear section of beat with no playing over the top.
I then went through a pretty tricky proceedure for a computer and math illiterate like myself. Separating each drum tone, then stringing them back together at the exact tempo to fit the track I was working on. I had to do this as my recording was no where near the right tempo. The result was this:
https://dl.dropboxusercontent.com/u/14720207/Tigers%20In%20The%20Butter%20-%20Sample.mp3Worth the effort? Arguably not. Lol. When my mate heard this sometime later he said, "Oh, I've got a plug in with all that retro stuff on it and it's got those sounds in it.". This presumably would have sounded a lot clearer and would have been easy to set to the right tempo and generally more time saving and effective. But that's how it goes.
These days, I hear Casio are doing great things and they probably always were. The unflattering opinions of myself and my young mates about casio were probably based on the crappiness of that kids keyboard we'd all seen. I mean, it only played one note at a time. My first Yamaha played four! FOUR man! The impressionability of youth.