Hi,
I definately think strain gauges are the way to go here,
either as someone pointed out hacking an cheap postal scale
or build your own. There are companies that sells the strain gauges
separately compared to complete loadcells ( not cheap as you've found out ).
The thing with loadcell are that they are fairly pricy as the also
( normally ) have temperature and linjearisation circutry inside,
not to mention that the mechanics ( housing ) is somewhat hard to
manufacture.
In your case you does not seem to have use for wide temperature spec.
So I would suggest purchasing separate strain gauges ( 4 recommemded )
amplify by an simple opamp ( perhaps with zero and gain pots for
'calibration' )
The maths to build an 'scale' from them are farily trivial and should pose
no major trouble.

Makes some searches for 'strain gauges' and it should turn up a few
directions.

Here's one to start with ( in Europe ):
http://www.hbm.com/

/Tony

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics