Re: Tunnel to Bell Island, here's a few facts I dug up -
Bell Island is 34 sq km in area, or less than half the size of Manhatten Island (87.5 km²), but larger than peninsular Halifax. It could possibly support a population of about 40,000 at suburban densities. Aside from that, it is only a relatively small part of the the available land in the St. John's metro area. Likely, a tunnel would only have two or three lanes at best, and would be prone to some congestion if 40,000 people were depending on it.
Distance to Bell Island - 4 km (approx)
A. Murray MacKay Bridge, Halifax - Total length 1.2 kilometres
Angus L. Macdonald Bridge, Halifax - Total length 1.3 kilometres
Confederation Bridge PEI - Total length 12.9 km (cost $1.3 billion.)
Lions Gate Bridge Vancouver - Total length 1.8 km
Port Mann Bridge, Metro Vancouver 2.09 km, including approach spans
Golden Gate Bridge, San Fransisco - Total length 2.7 km
Golden Ears Bridge (Metro Vancouver) under construction - a span of 968 m - to open in the summer of 2009 and has a fixed total construction cost of $808 million.
Although I just looked at bridges and costs, it seems like the estimated cost of $93 million is many times lower than what it would actually be.
^Map from Google
That's just my two cents, maybe someone has better figures on tunnel building costs - it depends upon topography etc.