Greg Hennessy wrote:

There are no hard numbers. Only various estimates, which are coming in
at between 1 and 2 billion dollars.

If you have *hard* numbers to present, we're listening.

I could not find a detailed estimate for the
robotic Hubble mission, but I have found
estimates for the past shuttle missions:

Hubble Servicing Mission 3A = $136 million, source:
http://hubble.nasa.gov/a_pdf/news/facts/FS32.pdf

Hubble Servicing Mission SM-2:
"NASA has spent approximately $347 million on
the Second Servicing Mission, reflecting the costs of
building and testing replacement instruments, ground
operations and other related activities. The Shuttle
flight will cost $448 million. Total = $795 Million"
source: http://hubble.nasa.gov/a_pdf/news/facts/hst-cost.pdf

NASA Cost Estimating Web Site:
http://www1.jsc.nasa.gov/bu2/hamaker.html

Simple and yet VERY USEFUL cost calculator:
http://www1.jsc.nasa.gov/bu2/SVLCM.html
According to the calculator the development cost of a
two ton "unmanned Earth orbital spacecraft" is $252
million, it is independent of the number of spacecraft
that are built, and it is about four times greater than
the cost of building one spacecraft, which is $67 million.

MY CONCLUSION:
1. The $2 billion figure is a gross exaggeration.
2. Building and launching three identical telerobots
costs as much as the development cost, so it
makes economic sense to launch three Dextre
telerobots and keep them busy.
__________________________________________________ ________

"NASA realized that if a shuttle crew could service HST, it
could be maintained and upgraded indefinitely. So from the
beginning, Hubble was designed to be modular and astronaut
friendly. The modular design allows NASA to periodically
re-equip HST with state-of-the-art scientific instruments
— giving the Telescope exciting new capabilities..."
source: http://hubble.nasa.gov/a_pdf/news/sm3b_composite.pdf