After unusual icy weather left millions of Texans without power, some are facing another crisis: Sky-high electricity bills.

The surge in pricing is hitting people who have chosen to pay wholesale prices for their power, which is typically cheaper than paying fixed rates during good weather, but can spike when there’s high demand for electricity. Many of those who have reported receiving large bills are customers of electricity provider Griddy, which only operates in Texas.

Among them is Susan Hosford of Denison, Texas. On a typical February day, she pays Griddy less than $2.50 for power. But...