Bottom line is that they're very different guns. The only commonality is that they both shoot .45 ACP, and have a similar mag capacity. This makes the choice even more subjective than the usual apples-to-apples comparison.
If he likes the ergos on the 4506, likes DA/SA, and thinks the trigger is OK, then he will be money ahead to go with the 4506. If he doesn't, then he will probably want to spring for the 1911.
Prices, as said, should be very different between the two. If they're not, he is either getting ripped off on the 4506, getting a beater 1911 (not always a bad thing), or getting a smoking deal on a 1911.
Mike