The price of second-hand Bitcoin ($BTC) mining rigs have jumped as much as $250-$320 in China as miners expect April's bull run to continue. CoinDesk reports some 220,000 to 700,000 machines will come online this summer with an expected hashing power of 70 quintillion hashes per second. According to TokenInsights, these second-hand miners can pay for themselves in about 200-350 days if current price trends continue.