I am interested in creating a private, secure virtual market that
facilitates semi real-time trading of unique investment properties. 
The number of trading participants would be fewer than 30, and the
number of properties virtually traded would be less than 20.  The
purpose of the market is to facilitate the exchange of information and
force opinion accountability by making traders ?put their money where
there mouth is.?  Think of Hollywood Stock Exchange, but fewer
investment properties and only open to a small group of traders.

I would like to know if there are off-the-shelf trading programs in
existence that can be easily customized to create this sort of
prediction market / information market.  I am NOT interested in
programs that tie in to existing markets such as NASDAQ or NYSE.  Part
of the difficulty of this search is weeding out the "Day Trading"
programs or other markets/exchanges that are not private and
customizable.  This is only valuable if I can create a distinct,
private market from scratch.  The software would ideally facilitate
normal trades (buy & sell) as well as more exotic derivatives like
selling short and call / put options.

If such programs exist, I would like to know how much each costs, and
where it can be found.