route throught wall or above the head ?

[Leonardo Boselli <leo@dicea.unifi.it>]

I know that the question is marginally OT, but since I have had everytime
useful responses fron this list i try again.
I need to connect a station in a recently built building, so recently that
until november cabling will not be present.
that station have to be connted with a server in another building.
I have to decide before tomorrow 26 if ask for a temporary connection that
would cost about 400 Euro or use an alternative setup: putting two
wireless 811b/g AP and use them to make a bridge. These aps (that i have
available, D-link 2000+) are given for 300 m in open space . the distance
between buldings is 380, with such apparates i have been able with their
plastic collinear to reach only about 100m, using a portable pc on the
other end. so i think with a better antenna on each end i could be able to
reach the 400 m (1 MB speed could be acceptable).
so the question i pose is this:
I could get line of sight but i should put the antennas in two difficult
to reach points of the two building; so it would cost some money and also
leave some of the apparates in uncontrolled areas.

I could use a directive antenna (i could get a 18 dbi one for almost
nothing) at the two sites, this would give me plenty of signal. but then i
would like to put the two antennas in a very easily and accessible place.
This give me three options: 
   a. connect two points that have at least 5 heawvy leaved trees between;
   b. "cross" trought the corner of another building, for a total of two
walls crossed at 30 and 60 degrees 
   c. usa a clear path but this would force me to put at one end
of the path a 2dBi antenna .....
what can i expect by the three options ? 
sorry for OT but i have to decide before tomorrow afternoon to order the
antennas _or_ the temporary connection ... (note: it _must_ work by 1
august !)