It's a Casio CTK-496. And in fact, when I Googled for information on this particular model, it still shows up as a model being sold by Casio on their website! So, I think the $55 I just spent was not a bad deal at all considering the retail price right now is $129.99.The CTK-496 includes 61 Full-Size keys, 100 Tones, 100 Rhythms, 100 Tunes, LCD Display, Dual Speakers, Transpose and Tuning Function, Microphone Input and Volume for Sing Along.
Craigslist -- ROCKS!
Honestly, this thing looks like it's hardly been used. I have no doubt that the original $75 the guy was asking was probably closer to the mark, but I am not complaining about getting the better deal.
Now, I must find some sheet music. I seem to have misplaced mine. And, I think I'll maybe get a beginners book for the kids and maybe give them some basic lessons. I know they are just going to love making music with it!