However, their precision in that price range is a little lacking.

Not sure why you think that.  Think you can do better ?

I think that the precision on a $10 scale is a little lacking because I require 0.005 gram precision and the $10 scales I found provide 0.1g or 0.05g precision.  The precision offered is insufficient for my needs.  I also need high repeatability, and the cheap scales either had poor or no specs.  Is the lack of precision due to the structure of the load cell or a limitation of the controlling ICs-- I don't know.  But since I found a $7 load cell as a component with known specs and that meets my requirements, I think that's a better option than going with an unknown salvage.

Do I think I can make a more precise load cell for that price?  Nope.  I don't even care to try.

LOAD CELL!!  That's what I was trying to find!  Thanks, Wade!  Micro load cells are what I need.  The ranges I'm working in are well below that of most scales available-- a few orders of magnitude smaller than kitchen scales.

I think I found my load cell:
http://www.phidgets.com/products.php?category=3&product_id=3132_0

And I found my 24-bit ADC:
ADS1210P
http://www.digikey.com/product-detail/en/ADS1210P/ADS1210P-ND/254605

Chagrin, thanks for the notes from experience!  If I could find an affordable load cell in the 0-10g range, 8bit would be OK, but even so I hadn't thought about that yet. If a 24bit doesn't do it, then I'll move on to another project-- ha. 

Thanks for all the input, folks.  It's time to wait for parts to arrive. 

My suggestion would be to buy some of the scales which operate in your range
and sell for about $10 on ebay,   and try to hack into their circuit somehow.

Otherwise, it doesn't seem like an easy problem.  There are force sensors that
exist,  I don't know how sensitive they are,  and you would have to rig some
kind of platform on top of them to hold the object being weighed, and then
calibrate it somehow.   Doesn't sound very easy.

That's great that it sounds like a difficult project!  The really easy ones tend to be less satisfying .  The other components of the project will be a geared-down DC motor to rotate a dispensing tube, and there will be an automatic dump when the correct weight is achieved.

I guess buying & hacking a $10 scale could help me learn how those interface.  However, their precision in that price range is a little lacking.

Does anyone know what the sensor component is called?  And has anyone used one before?

Hello, oh vast interwebs!
I'm having difficulty finding a new (to me!) type of sensor for my next project.  I am looking for a sensor that can measure small weights.  My range of mass must be as low as 100mg, must be up to at least 2000mg, and optionally up to about 5000mg.  Required precision would be 5mg or better. 
I'm not sure if I'm describing the specs right-- feel free to tell me I described it stupidly, if I did.

The sensor will be used in an automated dispenser as part of a small, non-commercial production line.  Unfortunately, the precision demanded can only be achieved by measuring weight, not volume.  And no, I'm not a drug dealer.   

My questions for all you wonderful makers in the world: what's the name of a sensor that measures weight?  Where can I find one that would be in the micro-weights I'm needing?  And has anyone used this kind of sensor yet with an arduino or raspi?

Thanks!
-A