There is pretty much ZERO probability of the E3 achieving payback of $1800 before ETH goes full Proof of Stake if the current timeline holds - it might have a faint prayer if ETH price DOUBLES fairly soon, but only due to it taking time for folks to "ramp up the hashrate" to match the price jump.
It was marginal iffy at the original batch price of $800 with VERY LOW electric cost.

There is also the outstanding question of "is it going to be reliable".

IMO anyone that pays $1800 for an E3 is going to LOSE money on the deal unless they have free electric AND they get a unit that runs for 2+ years without issues - and that is assuming that the other ethash coins don't fork and that coin prices stop SLIDING downward and even THEN it's still iffy if they'll ever earn their money back.