They actually took three planes according to Jake Tapper's blog. They took two G3's(Obama and staff in those) and one G5 (carrying the press pool).
I'd have to do some calculating, but I'm guessing if they did save any money, it wasn't a whole lot. They saved a little on fuel (maybe), but have additional maintenance costs for the three plane's 9 engines over a single VC-25A's five engines.