Well, unless he was a child living in Japan during 1997, he doesn't have the Illustrator lol.
So I assume you're talking about the Base set, the one that contained 102 cards and had stuff like charizard and blastoise and zapdos? The value of those really depends on several things. Number one is always condition; if they're not completely mint, as in no scratches on the holo part when tilted under a light, no bends, etc., then the value will drop a lot. The next thing to consider is which edition they are. If they had 1st edition stamps on them, then that's the best scenario for you. 1st ed cards are always worth more than unlimited ones (ones without the stamp).
Generally, Japanese cards don't sell for as much as English ones, but in this case you're lucky because the Japanese Base set does sell for more than the English set.
I would estimate that a MINT Japanese Base set could sell for atleast $150.