I would seriously look at a hi power clone, not sure of the price on those but I shot one last week and I was amazingly accurate with it. I want one so bad. Remind your dad that this gun will probably last longer than he will so it is a good investment and better to save up for something nicer.
My CZ75b was lightly used for $400~. I have been very happy with my little Bersa Thunder9 compact, but it was a bit more than the budget.
I say steer him towards used firearms in this price range. Maybe get him to handle a Ruger P95, not all metal-framed, but really solid and budget 9mm.
He loves ruger. He thinks the guns they make look cool. I showed him an add for a p95 for 350 and he wants to look into it(shouldnt p95's be around 300?)
I also told him to look at the sw9ve but he just hates polymer frames because of the one time he shot a glock he said they are just to light and uncomfortable. However he did love how the sr9 felt.