In other to ascertain if ethereum is very cheap to buy now,we may need to look at a brief history of how the coin has fared in the past.According to historical data on CMC https://coinmarketcap.com/currencies/ethereum/historical-data
Eth opened at $12.22 to close at $12.13 on 2nd july 2016,from here it moved to
 open at $8.15 and closed at 7.97 on Dec 31st 2016.
Eth opened at 7:98$  and closed at 8.17$ on  Jan 1st 2017
where it moved to a new ATH of
 of 53.58$ on march 25th 2017 closing at  51.25$, it doubled  to touch 129. 22$ and closed at 126.52 on 20th of May 2017. On 24th Nov 2017 it  touched ATH of 475.68$ closing at $466.28 almost at where eth is today,ETH journeyed to its last
 ATH on Jan 14th 2018 open at  $1397.48 closing finally at $1,366.77 from where it has entered a major correction to $434.03 13th July 2018. With this as a background, comparatively it is cheaper to buy Ethereum ,buy at each dip points if you plan to hold ethereum as an investment