I think being a ghosthead is a lot like being a Jedi. You gotta build your own saber/pack to be a TRUE Ghosthead/Jedi.
After being here for months, I've come to relize that if you plan on buying anything pre-made, expect a big pricetag, so even though you cant build crap, find someone near-by that can, tis what I am currently doing.
But also relize if one is going for a certain degree of accuracy, then some things will be better purchased. IE: A Bumper. Sometimes, if you can find em cheap enough, buying the piece will save hours of labor and headaches, IE: The spacer.
So, I believe that 75% should be done by hand, while you can fudge the other 25% with cash, that is, if you want your pack to look like the movies.