Nowadays, combined GNSS receivers like you mention are available from various electronic retailers for around 20-50$ a piece. The uBlox Neo M8 is a popular chip

Nowadays, combined GNSS receivers like you mention are available from various electronic retailers for around 20-50$ a piece. The uBlox Neo M8 is a popular chip, there are a few others too. They are widely used in UAVs (where I know them from) and a variety of other applications, and routinely use anywhere between 22-28 active satellites from multiple constellations (compared to typical 7-11 visible for GPS alone).