You may as well use aluminium. If it is intended for costume then go for it. If you want histiorically accurate armour then you need to pay for it from someone like Erik D Schmid. Even if you make riveted mail it won't have much in common with historical samples.

That's a good point. It's hard to do historically accurate rivetted mail. So if you're not going to pay the large $$, and you don't specifically care for the period weight, then aluminum can be a good way to go.

The weights you got from the calculator sound a bit off. I'm pretty sure my aluminum set is coming in under 20 pounds for both pieces, not just the hauberk. My steel hauberk (similar number of rings, and also 14 ga 3/8" ID) is just about 40 lbs.

90 lbs would sound about right if you were doing 8-in-2 (double mail) with 14ga steel.