I sat down and discussed this with my players. We considered using Archetypes as strong recommendations for what to purchase, but not generally as requirements. This is in order to allow some flexibility. Archetypes will have a cost equal to what the component Skills and Talents would cost - there is no discount, archetypes will exist only as a convenience (convenient once someone takes the time to put them together). Archetypes can exist for Home World, Career, Career Specialty, and pretty much anything else since they are not built to give mechanical advantage.
Characteristic Advances will cost 250 xp/500 xp/750 xp/1,000 xp. Skill Advances will cost 100 xp/250 xp/500 xp/750 xp. Talent Advances will cost 250 xp/500 xp/750 xp. This makes Skill Advances somewhat cheaper than Black Crusade suggests, and this is a desired change by our group. We have placed starting characters for a Dark Heresy-style game at 3,000 xp to spend.