It's been a while since I've bought wheels or thought about this, and I'm not an engineer or tool and die man by any means, so keep that in mind, but generally better quality aluminum wheel are lighter. IIRC, there are 3 basic methods of production; cast, forged and billet. Cast tends to be the heaviest and cheapest, billet the lightest and most expensive.
Cast aluminum wheels are the most common and affordable, and are produced via gravity casting, low-pressure or high-pressure casting. Gravity casting tends to be somewhat porous and weaker, and uses more material to compensate for strength. Pressure casting reduces porosity and provides a stronger wheel with less material, as compared to gravity. I suggest looking for pressure cast wheels if you can find that info, They generally will be lighter, better balanced and likely even a little stronger than comparable regular cast wheels.
Forged and billet wheels are made from better, less porous, more uniform gain material, and require even less material to achieve the desired strength, but these wheels are really above and beyond what you will want, or at least what I think you will want to pay for. $$$$
That is all off memory, so one of the engineer guys here will have to come along to correct/straighten out the info I provided, or you can search and read for yourself.