Free electricity you say? used Radeon 7970s, 7990s and/or R9 280Xes... they go for around 100 usd each (the 7990 can be tricky to find, but if lucky, fairly cheap). And downvolt every card as much as you can. My 7990 and r9 280 is downclocked to 950 mhz core, downvolted to 1 volt, from 1,2 which saves ALOT of power and reduces temps by at least 30%. each card makes 280 sols/s so ideal for equihash.. or if you want to go for XMR based cards cryptonote, its around 500 hs/card.


cheap budget rig that will ROI alot faster compared to any super expensive new card.