Do you know any good and tested weight sensors for small loads of 1-5 Kg ?
Have you considered opening up a commercial scale, and taking the load cell out? I’m not sure if that would be cheaper though. You could get some inspiration by checking out what types of load cells are in those things. Then you know what you need to look out for.
I have tried these force sensors before and they are simple to read and much cheaper than load cells. They come in different sensitivities but you have to be careful not to go over their limits.
http://www.digikey.com/product-detail/en/FSS1500NSR/480-2619-2-ND/1248954
Problem is how to mechanically deploy them…probably build them into a load-cell capsule…back to square 1 
Here is a high capacity one at Sparkfun:
This is what is typically in a bathroom scale with some kind of lever mechanism to divide the weight.
I would do what @Moors7 suggests and buy a cheap kitchen scale to get the load cell.
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