Much more than you could buy one complete from LMT, based on the very few complete parts kits I've seen over the past 6 years. As I recall, they were all used parts as well.
Why don't you just buy a whole one, and once it's transferred tax-exempt to your local SOT, have them split it up, or whatever it is you're wanting to do with the parts. That would certainly be much less expensive than getting piecemeal parts. You could sell the receiver as a Title I firearm, and keep the complete parts kit (and probably sell it too and make a profit off both if you desired). They're just less expensive as a complete unit.
Now regarding the standard handguard and mounting hardware, GI sights, etc. Those will all be cheaper on eBay, Gunbroker, and forums for sure. Those things are the most common components. Usually you can score spare barrels below dealer cost as well. 12" is more common.