You can use a P1900 from Carnetix to do this, but its overkill.
Since you've already got it working with an inverter, I won't suggest combinations that use old ATX power supplies or external enclosures.
A DIY option is to use LM317T linear regulators to output the power you need. Two in parallel will probably handle the needs of the drive (not sure, though -you'd need to check the power consumption of the drive). You can probably do the whole thing for $10 or $15 in parts.