Searching eBay on 500+digital+scale
will yield pages of choices costing less than $15, shipping included. I prefer the ones that use AAA batteries because the replacements are cheaper and easier to find. One minor caveat: Not all of the eBay ads state how long before the scale turns off automatically. If you're taring the cup for brew ratio
comparisons, the scale may turn off before the extraction completes. Some scales have a 1-3 minute timeout, others have a 30 second timeout.
Dan makes a good point. I bought a scale from Costco that has a timeout of less than 30 seconds and it is completely useless for coffee.
There are a lot of these things out there and the ones that I have bought have all been decent. All of this stuff is being made in China, and probably most of them will have similar components. You could even decide to buy two of them at a cheap price with the expectation that nothing electronic that costs $12 is going to last too long. These are disposable electronic devices, but if you can get a year out of it, then who cares?