The 'Transaction Fee' equals the Gas Price (i.e. 3 Gwei (shannon), or 0.000000003 Wei) multiplied by the Estimated Gas Limit +values.gas (i.e. estimated at 21000 for Sending Ether, and estimated at ~39401.25, or Estimated gas 31521, with buffer 39401.25, for Sending THIBCoin since its a transaction to a token contract).

I think the user should be able to set the Gas Price (as they can do already), but the label should be "Gas Price" instead of "Transaction Fee". And there should be another label called "Estimated Transaction Fee", which shows the value of (Gas Price * Estimated Gas Limit)

 console.log('estimated tx cost (ether): ', values.gas && values.gas.mul(toWei(values.gasPrice, 'shannon')).div(1000000000000000000).toString());