The complete collection on Steam costs as much as standalone SoA costs. I'm not sure why you still want to pay 40 bucks to get something you can get for 30.

It's the same bunch of 0s and 1s no matter where you get it from. It makes no difference if you get a key that enables the entire game or one that enables just SoA. All you're doing is flipping a digit in SE's database servers.