I would use a small transformer, they are very cheap in the sizes needed for these low wattage lamps.
A pair of identical lamps could be worked in series, but do not try this with 2 lamps of different sorts as they are likely of different wattages
You could certainly use a battery powered inverter with a 110/120 volt output at 50 or 60 cycles.
I would avoid high frequency inverters. I dont believe that the high frequency will be a problem in itself, BUT these are often intended to power flourescent lamps, and if lightly loaded may produce a grossly excessive output voltage.