If you have free electricity, you can do just like me : try to find some second-hand R9 290 as they will be cheap and their hashrate is great (but you already know that 
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Otherwise, RX580 are great if you can find it
)Otherwise, RX580 are great if you can find it
Yea, I tried to find more R9 290 but price is 280 USD or so each even used and I can't trust used cards. The price of a new RX 580 with 8 GB is around 370 USD and plenty available in Romania. With 6000 USD I think I could buy 14 pieces including 3 mobo+CPU+memory. That would make 420 Mh/sec (I already have 180 Mh/sec) which should bring 600 USD/month (total of 900 USD/month), just a little less than Vega 56 that would bring maybe 660 USD/month using Monero, but if I use Vega 56 for Ethereum that would bring only 340 USD/month..
If I do the step with Rx 580, I could add ~ 2 video cards a month to the farm, that means a 10 % increase. This results in a total of ~1800 Mh/sec in a year which will produce 2500 USD/month profit.
I have almost no cost for rig frames, because I sell aluminum extrusion which I buy factory direct per kilo, and the connectors I can print on my 3D printers at almost no cost because I produce my own filament.. so the costs of building the rigs can be neglected, besides the hardware cost.
