The prices of graphic cards are starting to drop. I'm starting to see GTX 1080's under $600.

I'm completely new at mining. I've only mined a couple of alt coins on my laptop. My question is, should I buy a new gaming PC with a motherboard that allows multiple graphic cards? When I'm not using the machine, it could be used for mining? Would buying multiple graphic cards over time be worth it? And would I be able to get a 100% return on investment before the end of 2018?

Any answers would be great. The other option would be to get an AntMiner instead of multiple graphic cards. So, what are your thoughts?