Hi,
it's been a while since the original request and I don't know if it's still relevant.
Actually, I can't imagine why on earth one might choose a CT-460 of all things (even out of all maybe-collectible Casios).
You're absolutely sure about the model no.? Most collectors who present their gear on YT show the CT-470 or other models that include the synth editor (the 460 doesn't AFAIK) and the weird sounds that can make.
That being said, the CT-460 actually turns up quite regularly on the German (I'm from Germay) classifieds site ebay-kleinanzeigen.de for reasonable prices. Shipping is often a problem, though.
A few current examples:
Kleinanzeigen: Musikinstrumente und Zubehör gebraucht kaufen - Jetzt in Monheim am Rhein finden oder inserieren! - kleinanzeigen.de
www.ebay-kleinanzeigen.de
60€; "very good condition"; offers shipping
https://www.ebay-kleinanzeigen.de/s-anzeige/keyboard-casio-ct-460/1978583233-74-8216
30€; looks good to me from the pictures at first sight, but only local pickup offered; unfortunately too far for me as well, but I could try to help talking the seller into mailing it nonetheless
Kleinanzeigen: Musikinstrumente und Zubehör gebraucht kaufen - Jetzt in Hennef (Sieg) finden oder inserieren! - kleinanzeigen.de
www.ebay-kleinanzeigen.de
60€; "very good condition"; same comments regarding local pickup apply as for the previous one
Please feel free to PM me if you need help with translation or (hopefully) talking sellers into shipping to Ireland.
CAUTION: Please note that with all consumer electronics of that age (1980-ish vintage) there are a myriad of potential (possibly hidden) problems that may be very challenging (more likely, impossible) to fix for non-technicians. From my experience (don't ask how many non-working AV devices I have collected over the years), this is a very serious issue. I strongly advise you to talk your son out of this idea, if in any way possible.
P.S.: I'm not affiliated with any of the sellers.