The Scottish tactician purchased a then-24-year old Cahill from Millwall in 2004 for around £1.5million ($AUD2.2m) and has reaped the benefits ever since.
Cahill's presence on the pitch for the Toffees during his time at Goodison Park has been vital for the Merseyside club and it has not been lost on Moyes who rates him above all the other players he has ever signed.
"As I've said many times, a lot of our team selection revolves around Tim Cahill," Moyes told reporters.
"He scores goals for Everton like [Frank] Lampard does for Chelsea, not quite in the same quantity, but he has done it over five or six years now. He scores goals every season and has been really vital for us.
"I don't think I'll ever do a bit of business as good as him again. There will always be business done when you pick someone up from the lower leagues but I don't think that will be done in the English leagues.
"You might do it abroad, but maybe not in England again because it's getting harder and the talent is identified earlier on in the lower leagues these days."