While I do agree that the sub can make a huge difference, I just think if it was me, I'd go the 'minus-the-sub' route. Otherwise he's initially compromising on the front speakers or the sub, and possibly both. Then a year down the road when he's saved up some more coin, he'll undoubtedly be bit by the 'upgraditis/what-if bug'. He'll be left wanting to upgrade his mains and it will cost him more money in the end than if he'd just waited a bit on the sub. Fight the disease.

"Chickens don't clap."