I just finished rebuilding/ modifying my 390 (from my '66 t-bird), so I know where you're coming from.
First off, the FE series isn't the cheapest in parts. Next in line are indeed the parts used. Quality parts will cost plenty of money for the good old "dinosaur"!

My personal, first time experience with my engine; it had been rebuild already...(back in the eighties as I found out, when I tore it apart)...
two different types of heads were slammed on, 30 overbore and rather worn out, so I had to go 60...8 to 1 CR rough cast slugs were put in...connection rods were of 3 different castings (but equal in strength though), some new gaskets and some liquid gasket was used...calling the whole thing a "power-pak"

To be honest, this kind of a rebuild is not the kind I would have spend my money on!
Can I do it better myself? I really don't know! However, you select every part you use after a more or less educated comparison of the available offers you get. (and asking around a lot!)
Then there's the matter of "being in control". Some want to be on top of things, whenever they are selecting any bit that might be used for their project. Others just like the thought that "more experienced" people are in control. You don't have to make the mistakes, they already made, so naturally, they will make all the right choices for you! (do they now? so when did they learn from mistakes made, surely not on customers' engines, did they?)

The build itself is ofcourse without warranty...but I have to say I liked working on it, creating something new and clean, from something old and greasy.

Like Don said,when it's time to fire up your newly build motor, it's the moment of truth! I too did hold my breath and cranked it over the first time this week. Heart pounding...Yes I was nervous!...but it fired up really nicely and ran strong for 30 minutes. I'll get back to you on reliability in a about a thousand miles, okay?