Yes, you can find half decent bathroom scales (100kg or so) in places like Aldi, Lidl, B&M etc for under a tenner. These contain 4 strain gauges and the complete amplifier / display etc. The baggage scales (~40kg) are pretty much the same deal except they only have one load sensor. You couldn't buy the bits for that price. The other cheap source is kitchen scales (~5kg) , if you need a more sensitive system.
When I say "sensor", in fact they usually have a dual strain gauge with elements at 90 degrees. Once you get into the details you will find that's actually what you want. The metal part has to be fairly compact and is typically a sort of spiral shape. I modelled one up not so long ago and in this picture, the element is where the yellow patch is and the force is applied to the blue spot:

The other thing to consider is that scales usually are measuring a load force, not a stretching or simple bending force, so the load cell element is not a simple beam with a strain gauge on the outside. It's worth picking up a set of scales just to see what the strain gauge system looks like – at as little as a fiver it's hardly an extravagance. Yes I've got a few….
Murray