I calculate the main prices of ETH and also BTC price regarding the mining process and costs. miners are the main people that affect the price of BTC and ETH. if the prices of coins will below the mining costs, the mining will not affordable. in general, if we consider the average prices of mining in all of the world, we conclude that the lowest prices of BTC is about 6000 to 7000$. and this amount for ETH is about 400$. so if ETH decreases more than 400$, the mining of ETH will not affordable and miners will migrate to other alts. so this migration will cause stopping the mining of BTC and ETH and also will cause the price of the transaction. in long-term, this causes the raising of the price for ETH and BTC.
Current price of ETH is really cheap, you can get in now if you missed the opportunity before. I ain't saying that it won't fall further, surely it can but nobody can predict the bottom and knows for sure. I am buying on every dip of 25-30% or so, if it's bottom I am glad and if not then I'm ready with my fiat money to invest more. Just remember that ethereum has so many apps built on it and several more coming and there devs are working on improving the transactions per second by implementing sharding.