I use EDD, which is usually a few mm different than prowheelbuilder. I've never run into any discrepancies with what the calculator suggested and what i ended up needing for a wheel build.

So, I'm curious as to where you're getting quality SS spokes for less than a quarter each, including nipples? My usual move is, say I need 36 spokes at 268mm, and 18 at 266mm, plus 18 at 264. I'll get 40x268, and 20 each of the 266 and 264. That'll give me a few extra for "just in case", and it costs me $20 plus shipping. With nerps. I don't know about you, but i regard having an extensive "spoke library" as a dangerous thing, as I'll find myself trying to use the excess spokes to build some wheels, and then i try to find a frame for those wheels.... next thing I know, those extra spokes have snowballed into an extra bike....