Probably not even that complex or expensive if one's looking for a lightweight HUNTING rifle. Just go with a traditional styled stock with either pillars or action block installed. Since hunting doesn't often involve a lot of shots and barrel heat is not a factor, a heavy sporter barrel will most likely be adequate.Wouldn't be to hard to build a lightweight rifle.
Use one of the Titanium actions
Proof research barrel
Manners/McMillan hunter stock.
Then use a high end hunting scope.
Should be pretty light. Probably to light for my liking.
Kind of hard to build a "lightweight" rifle if using heavier barrels. Some of the heavier profiles weight 5-6 lbs alone, before action, stock, scope, bipod, and other gizmo's.