Filling in a sunken living room to level of other floors
One way to raise the floor, and possibly the most reasonable cost wise, is to install what I would call sleeper joists sitting the top of the existing subfloor and than add new subfloor covering over those. 

These "sleeper joists" would be installed as 2xX material on edge. This could be 2x6 planks spaced 16" apart. It may be necessary to rip the 2x6 planks to somewhat less than their native 5.5" width so that the subfloor and whatever flooring that you choose to put on top of that would match to the adjoining floor heights.