There is only one way I know of to logically guesstimate where a bottom could be based on past price action. I believe bitcoin -0.19% is reverting to its 200 week mean average range which will be anywhere between $2500 - $5000 (probably somewhere in between). The time in which price reaches this range matters, as it has to correspond with the trend-lines, and/or orange and red moving averages as shown in the chart. The last ~80% drop (from peak to trough) lasted 419 days. It's extremely unlikely we reach near that number again... but it's the only number we could use to project a possible bottom. With that number or range in mind, it would mean a bottom sometime in late 2018 or early 2019 -- January 2019 if using the 419 day peak to trough as a metric, followed by a consolidation phase (in a bull market it can be considered an accumulation phase). We are still very much in a bull market looking at this picture from a distance (10 - 20 years).
I think the best strategy to try to buy cheap is to have resting orders sitting at specific prices. For me, they are $4200, and $3100. These are my weekly bids. I may have other orders depending on developing price action as we continue to watch the price unfold.
It's still possible to even break an all time high this year... but it seems unlikely to me. In my opinion, to have a sustainable run in the next 4 years toward 60k or 80k per coin, it would probably require more downside and longer term consolidation. I think we could bottom sometime in September 2018 based on the trend-lines drawn and where price should correspond with those trend-lines in terms of time.