Thing of it is, every smith is different in their approach and "touch" when it comes to certain guns. 1911's are definitely one of those guns. So two smiths may actually tune the same pistol in different ways, one may use/modify existing parts, the other may use off-the-shelf replacements he thinks are better suited. Ultimately there are so many different ways to improve a 1911, I'm certain you can get the same results but the question is how much money and labour is involved with a particular shop. A Nork straight from Armco is already worked-over, the work itself is a known quality to many shooters here and the cost is worked in to the price up front.
I'd say for a cheap beater or project that you want to do yourself, buy from wherever is cheapest. If you want a 1911 that'll shoot reasonably straight without being too pricey, the Armco option is a nice one to have.