You don't even need to guess. There are real hard numbers above.
The latest Western Canada Tesla projects were government funded (50% total costs) and the funding is public information. This includes all equipment costs - utility transformer installation, excavation, conduit installation, concrete work, 480V autotransformer installation, disconnect/breaker cabinet installation, Supercharger cabinet installation, Supercharger stall installation, bollards, signage, re-paving, and commissioning - the whole project.
They built 3 sites each with an 8 stall Supercharger plus "bonus" third party 50 kW DC fast charger (required for the funding) for $794,459 CAD total funding (this is the public 50% funding number). The average 100% cost for one site is this divided by 3 times 2 or $529,639 CAD average for an 8 stall Supercharger PLUS the bonus third party DC charger. In US dollars this is currently $421,982 USD. So less than what you estimated for a 4 stall Supercharger. And given that the 50 kW DC fast charger, 480V autotransformer, and installation for said charging station by itself is about $100K CAD ($80K USD) that would put the 8 Stall Supercharger including all other equipment and installation costs at roughly $382K USD.
The 3 sites on this project are Cache Creek, Quesnel, and Williams Lake.
Now, I know that Tesla doesn’t have a Supercharger planned for Cache Creek in 2020. However, I found a document from a council meeting from September 16th 2019, saying the town was looking to install a Supercharger station (unknown number of stalls) at the Tourist Information Centre, which...
teslamotorsclub.com
Hello, No, thank you. Build superchargers in Quebec please. Goodbye
teslamotorsclub.com
Thanks to TeslaMcQueen for the tip-off. 8 Stalls under construction at Prosperity Shopping Centre in Williams Lake, BC.
teslamotorsclub.com
There was another government project with Tesla, but that project didn't have consistently sized sites, and had more third party charging stations per site so isn't as easily isolated like this project.