Depends on your usage and how long you want the batteries to last, generally anywhere from ~5k USD for a day's worth of backup power (using average-ish USA resi

Depends on your usage and how long you want the batteries to last, generally anywhere from ~5k USD for a day's worth of backup power (using average-ish USA residential consumption, adjust accordingly) to 75k USD for a week (assuming you're using quality LiFePO4 cells with a good BMS).