It is impossible to predict the price of Ethereum in 2018, I mean for the whole year. If you ask what the price will be in January 2018, then I would say it should keep the same range — $200-$400.
However, certain events may support Ethereum’s price.
The most important event is Bitcoin’s hard fork planned for November 2017. After the fork, a new coin will be available — it will be called Bitcoin2X. The fork is referred to as SegWit2X. The miners that support this fork say that the after-fork blockchain system will become much faster and more flexible. It seems that 85% of the Bitcoin community support the fork. Big exchange sites like Coinbase support it too (Coinbase is directly connected with the fork initiators).
Anyway, the key thing here is that no-one knows how the fork will behave. We will actually have another Bitcoin after November. The unpredictability is very frustrating. Before the fork, Bitcoin will keep surging because investors like to get free coins. Each hard fork is an occasion to get free new coins. For example, recently, during the Bitcoin Gold fork, Bitcoin owners got an equivalent amount of Bitcoin Gold. The bad news for them is that Bitcoin Gold fell by 3 or 4 times immediately after it was released.
Bitcoin2X futures price is around $1000 today, which means the coin will have great value after November’s fork. It won’t happen as with Bitcoin Gold because Coinbase and the media will support it at this time.
If something fails with the fork and people lose confidence in the way Bitcoin is approached, they will move to Ethereum — Bitcoin’s biggest rival, and here is where Ethereum may surge. It may double or triple, which is very probable.
Besides, Ethereum has good fundamental value because of its smart contracts and blockchain functionality to create other tokens as layers.
So — if the Bitcoin fork goes wrong — Ethereum will jump, and in 2018 we will see Ethereum price beyond $1000 maybe.