In future miners will be rewarded almost exclusively with transaction fees.

The idea is that bitcoin is widely used with millions of transactions on each block, so those fees will be enough.

So theoretically, if Bitcoin really become adopted as we expect, the prices are very low now as the reward is 12.5 BTC for each block plus fees (every 10minutes). The next halving will reduce to 6.25, which will probably lead to a great price increase