According to sources speaking to Android Police, Google Home, a voice-controlled speaker similar to the Amazon Echo, will use the company's Google Cast wireless multi-room technology to connect to other Google Cast speakers and Chromecast products, and will be priced at $129. This is also the likely price of a new Wi-Fi router that Google reportedly has in the works.
The 4K-supporting Chromecast Ultra meanwhile is rumoured to cost $69, double the price of the existing Chromecast (£30). It's likely that the cheaper Chromecast will remain available due to the relatively small adoption (yet faster than HD) of 4K televisions.
All will be revealed at the Google event on 4th October.