Im pretty sure they will be a bit more the marginal, its not always about how loud something is if you get a screaming tweeter blowing your ear drums out in a bad way. Factory speakers for that car are borderline horrible. This with the proper HU will make a world of diffrence.
I would never amp my speakers with a budget amp. They need the best signal you can get. And with his budget of $400, your talking about some cheap(hifonics) 5.25 and a budget amp. So if he has a good HU, its the best signal he can get right now!