What is the possibility of technology like Google's balloon reducing overall connectivity and internet costs?
I doubt it, let's take a look at Project Loon from X (previously Google X):

The balloon is to be flown at an altitude of 20km (about 65,000 feet). The balloons cover 5000 square kilometers (about 1930 sq miles). So the balloon and its service (red triangle) kind of looks like this:



The full length of (a) is 60,000 meters (60km). Assuming the ground area is circular, the area of service at the ground (b) is about 94.9km in diameter. So you need to figure out what the service area is at 40,000 feet (about 12.2km). I won't go over the math here (that is for a different section of SE), but you get:

Beam Angle at the balloon: 134.2°
Length of (d): 37km
Service area at 12.2km: 1075 sq km

So the problem here is that the balloons would have to be spaced much closer since the (d) of the balloons would have to overlap to give continuous service. At the speed of an airliner (550mph, or about 885kmh) the airliner would speed through the 37km wide circle (assuming it takes a straight line through the center) in about 2.5 minutes. This is either hindered or helped by the balloon speeding through the stratosphere (Project Loon's record is currently 162kmh). So you would pass through anywhere from 3.1 minutes (with the balloon) to 2.1 minutes (against the balloon) worst case. 

So looking at it from purely an "is it possible to provide internet service by balloon to airliners" perspective, I would say no, not economically anyway. You would need roughly 3 times the number of balloons to cover the same area at altitude as you would be on the ground. The balloons are designed for ground service, so if airplanes did use them, they would have to switch back and forth from satellites and balloons every 2-3 minutes.