So since you asked, I went and grabbed the copy of the article I have in my notebook as originally I was planning on copying this very build in my original plan for my dart using one of the spare '70 318s I have. I eventually decided to go big block since the cost to build was actually gonna be cheaper to exceed the horsepower I wanted.
Now when I say astronomical, I'm referring to this combo. This is a combo found in the April 2004 issue of hot rod magazine. I'm sure it is NOT THE ONLY combo out there but this is the combo I had in mind when I made the "astronomical" statement that seems to have sir rumblefish all stirred up. When you look at the cost it'd take to do that these days, the cost per horsepower is astronomical if you're comparing a 400 hp 318 vs the work for a 400 hp 360.
The parts list isn't what shot the price up in the 318 they built per say but rather the extra machining costs. For example, they had the bores notched, I'm assuming for valve clearance to cylinder wall issues, a 360 will not need that. According to the price list I have from the shop that did my 440, cylinder bore notching is 150 per cylinder. So add 1200 extra to the 318 already.
On top of that, they used a set of fully ported heads with bigger valves. There's easily another 1200-1500 bucks. Now before you say they'd need to do that for a 360, well not necessarily as there are some magnum headed 360 engines breaking the 400 hp without porting. Hotrod even did such a build in their February 2005 issue, which I also happen to have.
They used stock magnum heads on a 9.5:1 compression 360LA block that were re drilled for the LA intake pattern. They drilled the new holes themselves according to the article, so no added cost there.
Rest of the parts are similar enough price wise to that of the 318 parts to not matter for this argument.
So let's call it 2500 extra for the 318 build. That's nearly double what'd it'd cost in parts and labor for the 360. So call the total build around 5000. So 5000 to build a maxed out, 401 hp at 6350 318 vs a 2500 dollar 403 hp at 5100 rpms 360......
So I stand by the notion that the 400 hp 318 I was referring too in my original statement. Paying double to net the same result is astronomical to me.