Always been billed with the 1.2 rate.
And that has steps of 1 to 150, 151 to 400, above 401 kWh.
Average price overall is about 4.6 Baht/kWh (using near 400 kWh).
500 Baht would be roughly 100 kWh or 100'000 Wh.
A fan typically is 50 W.
100'000/50 = 2000 hours running fan would equate to 2000/30 = 66 hours/day