On amazon there's still the occassional evga 1080ti sc2 for $830 and some MSI/Zotac models below $800, but they sell out in a minute.
Must be fast!
Yeah..
Not only on Amazon, also another online store very faster sold out if price normal or cheaper from another seller.
R9 390 ( 34 mh/s but nearly 300w )
At 2017, I buy secondhand R9 390 8 GB priced $170 on the Online store. The shortcomings of this GPU is heat and the hungry power consumption except someone have doesn't problem in electricity (cheap or free).
For the R9 390 to be profitable, you have to undervolt a lot.