400-450 hp is easily accomplished with an LQ9 w/ heads and cam. Cost effective I'd say that is it, but take my opinion w/ a grain of salt. I know what I'm talking about, but I rarely do anything cost effective lol. First LS1 I built made 842 hp on juice. But I have heard of quite a few F-bodys making those #'s with a 6.0L w/ heads and cam. My cousins T/A made 470 something like that. And he did it just a cunt hair over 3K, w/ him paying to have it installed.