what he said....the only way you would have a noticable difference in cost would be 277/480(commercial, industrial)Power(Watts) equals Voltage (120/220) times (*) Amperage (Amps). A 220 v light uses the same power as a 120 v light if they are 400 watt lights, they do not burn brighter or do anything different from an end user standpoint. they are a tiny bit more efficient because most electrical things have less losses at higher voltage levels. You won't notice anything on the bill, maybe $1 a month difference. Most ballasts can be wired to run on either 220/240 or 110/120.
240v is good for multiple light ops. being that you draw only half the current, you can run twice the lights on a circuit that a 120v circuit could handle.
1kw 120v = 9.5 amps
1kw 240v = 4.7 amps
these are for my ballasts; results may differ.
if you ran the same 20 amp circuit / same 12 gauge wire only this time wired for 240v you could run 4 lights .