a well tuned ion most cetainly is not a gas hog....and yes, you should get more than 3 pods.....my memory says around 400-500 balls for that...although if your 3 pods + a hopper you're not too far off the mark.
a little tuning required, so:
2 questions:
1) is your ion stock? if not, what has it got as ups?
2) is your ion tuned? most importantly have you set the dwell for yourself?
the dwell setting is one of the biggest factors in determining your efficiency - a high dwell will mean that you will use more air, cylce a little slower, but gain more shot to shot consistency. it's all a balancing act. you can setup so that you can shoot for ever (but slowly) or more consistantly, but less effeciently.......