Reading replies here, sounds like the problem to get HA on budget are decent power consumption and miniaturization.

I wonder if coming up with a earpiece-with-smartphone like combo can be a solution? So the main device with the battery and signal processing SOC is separated from the earpiece. This main device can live in a pocket or attached to the user's belt, while connected to the earpiece through wire.

Perhaps no the most convenient solution, but would it be possible to make such device available cheaply off the selves?