Reinvested Cost Basis. When you reinvest dividends, you buy the stock at a different share price than you originally paid. For example, if you bought a stock at $20 per share and you bought 100 shares, you invested 100 times 20 for a total of $2,000. The cost basis of your investment was $2,000.f you reinvested dividends in a stock before you sold it, you changed your cost basis. In the example, you originally invested $2,000, but you reinvested $200 in money you received from dividends. Your cost basis rose to $2,200.