I know that the cost of a transaction is
gasUsed * gasPrice.
Gas used cannot really change unless you change your smart contract code or the gas cost of EVM opcode.
So the gas price is currently
10gwei, it's almost nothing but smart contracts are getting more and more complex and even though I follow Eth news everyday and own Eth, am not willing to pay $1 to execute an action on a DAPP.
That's why I think very low transaction cost is really necessary in the future (even maybe free) for mainstream adoption.
TLDR: What will be the gas price when Eth uses Proof Of Stake ?