Some maps I've found that might show one of the reasons for the north segment's costs going up, as it is normal practice to not run utilities under rail, except for perpendicular crossings. The freshwater pipe under centre street is more than a meter wide under the street. :
:
A major (AER regulated) natural gas line at Centre just south of the bus trap complicates things in a pinch point (I suspect the shape file doesn't show the exact location, just the general one:
Add in sewer and storm water on top of that...
For storm water, there is an outfall into the creek between the Centre St Bridges, that I suspect comes from a line running Centre Street:
Which if it drains things in the watershed that flow towards it, and the storm sewers parallel that huge main are indicative of the outflaws watershed, may mean that outfall drains a fair portion of the NE Nosehill runoff, let alone the neighbourhoods (the blue line in this map is the division between watersheds)
With a split roughly here, with land south/east of roughly the red line draining to that outfall (I don't see any evidence of another outfall sharing the work in the area):
Adds up to Big $$$