Steve Faber used to sell a unit like that. It just captured the peak microstrain reading. That's pretty straightforward to do, and can be done quite economically. I think mine is still kicking around somewhere. He did some good work on that product.
For whatever reason, the Faber unit had less precision than the PressureTrace. I think it probably related to circuit board layout and such. There are some tricks to excluding electrical interference, such as using a two layer board, with one surface being used just for ground.
You can get strain gauges for $5 if you shop. Some of those are not sealed, so the user will want to cover them in nail polish. But that's one way to keep cost down.
