Conservatory and Bonus room are about 200 sf each and cost $25,000 which is a cool little $125psf which drops the average cost psf.
Note that you "lose" your covered patio which was livable space before (not counted towards original sf). Nonteless, for plan 2 it makes so much sense to have the conservatory to have your main dining area. Also, there's such a long streach of window that brings great light in the house.
Bonus room is great for another living area for kids or an office is you close it. Worth every penny IMO.