if you are diligent and scour ebay constantly you can find some good deals on s5.. there was one earlier that went for like 360 shipped
But 360 isint that much of a good deal since thats a massive 1.75BTC. The ROI on that purchase would take a very long time if possible at all, currently.
yeah maybe 5-6months depending on electric cost.. but thats about the closest ive seen to bitmains last price which allows one to use a credit card to purchase.. although zoomhash now has the 3 pack for like 1100
Or 1 year + with the current difficulty increase trend, hard to tell.
With the S7 around the corner, its probably better to wait for the mass sell. Just since the new chip announcement the market place already started having tons of S5 for sale.