Today!Merchant have 90 Second-hand Z1 machines for USD$2,200 to me, but ROI needs 110 day and profit is drop so fast, finally I gave up to buy it.
What merchants are selling for $2200?
CNY 15500 around USD2200 Free Power Supply
Expect a sub $2500 fire sales on Zig Z1 soon from all vendors.
100 days, not gonna happen. Basic rule, add double the amount on your calculation day for an Asic and you are most likely there +- some days. And this only includes the difficulty increase, not an upswing or downswing of the market.