It is not so much the pedal frame material that matters, but the bearings. They should have sealed bearings and should be smoothly-rotating. Not the kind where you feel a bit of notchy friction when rotating them.

Plan on spending at least $50 for a good set of pedals. You'll thank yourself later. It's a shame to get a nice bike, then throw away a bunch of energy on pedal friction.

For this purchase, I would go to a bike shop and try them by hand. You'll see what I mean.