The 1000mi supercharging credit is actually 400kWh, which with the Model Y's rated range is about 1625 miles. Valued at $120 for my areas V3 Superchargers @ $0.30/kWh.
In actual usage, I spent 321kWh to do a 1150mi road trip, about 280Wh/mi. I added 300kWh via Superchargers, and spent $82.38, an average of $0.275/kWh (about 2.5x more than my home cost).