Now I'm thinking something like this for the amplifiers and we could run the whole thing off one lipo cell.
https://www.mouser.com/ds/2/405/tlv2772a-449371.pdf
https://www.mouser.com/ds/2/405/tlv2772a-449371.pdf
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I think you need to spend a lot more then $10 to get anything good.There are hearing aids available on ebay from under $10, with tone and volume adjustment (I only saw a single dial, so maybe this is untrue).
If desperate, there's a slim chance that they're usable.