You're starting with what is now the obsolete AR10/AR308 original style platform. Getting to 8 pounds isn't easy or cheap. 3K is about 1K more than what is currently offered. I don't consider that cheap. The platform you really want is the DPMS GII as you can get to 8 pounds with a medium heavy barrel and normal furniture etc, just by replacing the handguard. It's also smaller in size so it's handier. That's really what you want as a base. But... it's restricted.
The design of these rifles is really from battle rifles of old. The FN Fal for example in a lighter configuration is about 9.8 pounds. The M14 was about 9 pounds without a mag. Lighter became the thing with the 5.56 and progressed to today's CQB etc firearms. The AR10 continued to be relevant as a designated marksman rifle. Not as a battle rifle. Fully kitted out with scopes and bipods these things are weighing in the 15-16 pound range. This includes the HK that just won the contract to replace the KAC with the US. The LMT MWS used in Afghanistan is about 9.8 pounds empty with a shorter 16" barrel.
Lighter and shorter etc is better. But again trade offs. What you are asking for isn't really the strength of the platform as adapted for recent use. The newer platforms based on this older one have gone to weight and size reductions. I think your expectations are based on those and not that you are working with the old system.
Yes, you can build a light weight with parts designed specifically for that but it will as you even pointed out, cost more money. Plus it's a compromise. You won't get a good 8-8.5 hunting style Stag 10 that is also acceptable to target shooters. Weight is usually the tradeoff between accuracy and mobility/light.
I know a lot of guys want this all purpose rifle. But keep in mind an all purpose is usually a no purpose. It won't do anything that well. Once you start specializing especially with weight reductions, the costs climb.
I'm happy with what they offer right now. I generally prefer a more DM/target orientated AR10 rifle myself. I have the Gii for a lighter weight Reece style rifle. If non restricted this would be the way to go for a AR308 semi auto. It's designed from the beginning to address those very goals. The old style isn't, unless you want to go very retro with the first ones. Ironically that very goal of super light cost Armalite the military contract when their aluminum alloy barrel blew up, which let do the M14 being accepted instead.