Since you want to invest 8000 USD for Ethereum mining now in a time when mining is not as profitable as it used to be I am assuming your electricity in your country is cheap.
For me personally the best thing to do is to buy 4 rigs with 6xRX580 8GB cards with modified Bios. This is the best setup for you and you will have quite a good amount of profit in a month.
This is if you buy new rigs, if you buy used ones you can buy even more than 4 rigs.
4 rigs with
6x RX580/8GB (24cards toltal) going to cost you more than 8000$
![Smiley](https://bitcointalk.org/Smileys/default/smiley.gif)
You need
24 x RX 580/8GB (with modded bios without killing your cards you can get 29.5MH/s easy)
4x PSU (min gold rated 1200w+ , dont go for a cheap ones i would suggest 1500 or 1600 watts psu's)
4x mobo
4x cpu
4x 4GB mem ( 8gb Better )
4x HDD ( SSD better faster )
24 x risers
4x open Frame
This would be closer to 9000$ ...
Im not sure about your electricity rate lets calculate first with 0,1$/KWh then 0.15/KWh and average 1000watts/rigs
BUT !!! Keep this in your mind :None of those calculators you are seeing on the web can tell you what's coming tomorrow , months later , 6 months later or a year later !
Those calculators telling you about today , at that moment when you typing in your information ! as soon as the difficulty , ETH/usd exchange rate changing , those numbers are not valid anymore ...
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