The ADS1299 from Texas Instruments:

https://www.ti.com/product/ADS1299?utm_source=google&utm_medium=cpc&utm_campaign=asc-dc-null-44700045486650716_prodfolderdynamic-cpc-pf-google-eu_int&utm_content=prodfolddynamic&ds_k=DYNAMIC+SEARCH+ADS&gad_source=1&gclid=Cj0KCQiA5-uuBhDzARIsAAa21T8xqXaoUs3HyoRCnh9rvpEDo6Ho4ed8YzNxHo1rvCK-8np0HERaducaAniBEALw_wcB&gclsrc=aw.ds

ADS1299 data sheet, product information and support | TI.com:

The ADS1299 from Texas Instruments is a chip which is mainly used in EEG devices. It never has been cloned. Peter Gamma from www.petergamma.org supposes that EEG devices which contain the ADS1299 chip are part of a marketing trust to keep prices for EEG device high, and want to maximize profits from EEG devices.

Also the OpenBCI made in China products increased in price in recent years.

• A view years ago, they started at 230 USD for a cable version module.

• But we did not find this cable version anymore.

• We now found only OpenBCI made in China products starting from 340 USD:

On the other TGAM EEG modules:

have been cloned, the price has dropped from 20 USD to 18 USD on Aliexpress in recent years.

And the ADS1115 16-Bit Analog-to-Digital Converter:

has been cloned as well, and can be found for 5 USD on Aliexpress.

With these cloned components it is possible to build up a EEG device with 8 channels for around 230 USD. This was the starting price for OpenBCI made in China.

But there is a tendency for products which are based on the ADS1299 to maximize profit out of it. With TGAM modules and the ADS1115 16-Bit Analog-to-Digital Converter it is not possible, since both electronics components have been cloned and have a clone competitor.

And Home Assistant which can run for instance on a Raspberry PI, here in the example of the Apple watch is free:

Apple Health Daten in Home Assistant visualisieren

With all of these components we can build affordable multi-sensor EEG devices by ourselves. And the prices for these components should be stable.