There definitely could be one out there, but given the size of the Apple charger, power output performance, build quality and ubiquity, I think it'll be hard to

There definitely could be one out there, but given the size of the Apple charger, power output performance, build quality and ubiquity, I think it'll be hard to find an alternative that costs less. A lot of expensive components goes into making this charger. I can tell you from my experience of trying to build a similar supply, that's not even an AC-DC circuit, that the components alone cost $30 USD. Even at Apple's production scale, it'll most likely still cost ~$20. That's 25% of the retail price. I'm constantly amazed on how they manage to make them so cheap! But all the attributes I mentioned could be irrelevant to many. If you carry a 30 liter bag around, double the size of charger won't make a difference. If you're powering lights, output ripple doesn't matter much and so on.