Bitcoin has fallen back below $84,000 after touching a September monthly high of $87,500, according to CoinDesk analysis. Data shows that investors who bought in 2025 have an average cost basis of approximately $88,000, meaning these buyers are currently at a loss. Their cost basis could form a key resistance level due to recent selling pressure from other buyers. Additionally, the average cost basis for U.S. spot Bitcoin ETF investors is around $82,300, a level that could provide support if Bitcoin experiences further declines.