Drawing more amperes doesnt really mean more costs. Our PUB watt meters register the true power(W - watts) and not the apparent power (VAR - Volt Amp Reactive)as measured by the clamp meter.
Magnetic pumps do have significant inductive load so it will actually draw more current than required. However good quality pumps should have a higher power factor.
Running poor equipments with poor power factor will not increase the electrical costs directly but it does have negative effects.
The excess amperes will heat the wires and internals of equipment, resulting in higher heat load.
The excess amperes will burn poor quality electrical products, I had my power extension burned when the MH capacitor came off!
Drawing 6amps for 2x250watts is indeed too high .. more than 2x my intake. Here's an article I wrote abt power factor correction.
http://www.arofanatics.com/forums/showthread.php?t=136250