With Bitcoin poised to reach its all-time high price, we set out to search for efficient crypto mining companies to invest in.Based on 2021Q1 QR, Riot was the most inefficient mining company where its total mining cost is 50% higher than that of MARA and BITF.We revisited Riot's 2021Q2 QR and found that RIOT's total mining cost remains consistently high, coming in at $34.475k per BTC or a 3% increase QoQ.Given our assumptions and Riot's 2022 forecast, our valuation framework values Riot at $861mil (65% overvalued), BITF at $850mil (13% overvalued), MARA at $2.265bn (36% overvalued).65% overvalued may seem exaggerated, one supporting evidence is Bitcoin's rebound from the July low ($30k) has led to the recovery of BITF and MARA but not Riot.