To me, that seems like a tall order to have a good digital scale under $100??
I would say that good is one that holds zero and didn't drift and is repeatable.
Have not had much experience with too many digital scales, I do know that I would not want one that is powered only by battery. I read a lot about them loosing their mind when the battery get a little low? How low is low ???
I use the rcbs chargemaster 1500 and have had it for several years (5 or 6 years?) Has worked great so far.
BUT...There always seems to be a problem with a few of the better ones too. They are mostly made with cheap china electronics IMHO.
I've read reviews by some which say they are great and some say junk?
I'm sure others will have more experience than I on this subject.
I just tend to think better quality for important tools in reloading. ( Just me?)
Do a lot of asking questions like you are doing here, and research online stores like Midway and all the others for reviews. It's what I did long ago and for any important purchase I make before jumping to buy one by manufactures advertisements only.
I tend to keep my 10-10 beam scale on my bench at all times no matter what.
It has never let me down and no batteries or power needed. But the owner needs cheaters (glasses) to read it these dayZ. Digital ones are nice with the large numbers....! ( If they are correct?)
Good luck.
TxDon