No one's buying an S5 for $100 in five months. In five months they'll be junk. S5s are currently going for $160 on the forums now.
i wouldn't say they will be junk there is always a market for them. No new hardware is/has been announced and validated so right now s7 and s5 are tier 1 and 2 as far as latest and greatest. sure the rising diff and 1/2ing will impact them but those in free or super super cheap power area will still use them or those that want to throw them at the solo lottery. look at the USB miners that are still made people snap those up instantly.
There is new hardware coming from at least two manufacturers in the next 60 days. We've got a lull in the hashrate here, but you'd be fooling yourself if you don't think even S7s are about to become old technology.
Where do you see new hardware coming to the small user within the next two months? All i saw is SP and Bitfury considering private investors.