Web3 sendSignedTransaction Transaction cost

Question

I'm new to Ethereum world. I've just manage to create an example that calculates transaction fee and sends a signed transaction without a contract using Web3js library.

My issue is that my test account is running out of balance pretty quickly. I must be doing something wrong. I did this transaction: https://kovan.etherscan.io/tx/0x5cb10c454d8d331e35ba3812522ea9cd5b82fdb7ecde75c5b48ec1550d99cc98

If you see the details:

Value: 0.000106 Ether ($0.00) 
Gas Limit: 21000 
Gas Used By Txn: 21000 
Gas Price: 0.000106 Ether (106,000 Gwei) 
Actual Tx Cost/Fee: 2.226 Ether ($0.000000)

I see the actual transaction fee is 2.226 Ether!

I'm calculating the transaction fee as follows:

var transactionObject = {
  from: sender,
  value: amount
}
w3.eth.estimateGas(transactionObject, function(error, gas) {
  w3.eth.getGasPrice(function (error, gasPrice) {
    var gasPrice = Number(gasPrice);
    var transactionFee = gasPrice * gas;
    console.log(transactionFee);
 })
});

Then this transaction fee, I am using it on my transaction:

w3.eth.getBalance(sender, function(error, balance) {
  if (balance < (transactionFee + transactionValue)) {
    reject("You don't have enough balance to cover this transaction");
  } else {
    w3.eth.getTransactionCount(sender).then(function(count) {
      var transactionObject = {
        nonce: w3.utils.toHex(count),
        from: sender,
        to: receiver,
        gasPrice: w3.utils.toHex(transactionFee),
        value: w3.utils.toHex(transactionValue),
        data: ''
      }
      w3.eth.estimateGas(transactionObject, function (error, gas) {
        transactionObject.gasLimit = gas;
        var tx = new Tx(transactionObject);
        tx.sign(privateKey);
        var serializedTx = tx.serialize();
        w3.eth.sendSignedTransaction('0x' + serializedTx.toString('hex'), function (error, result) {
          if(!error) {
            resolve(result);
          } else {
            reject(error)
          }
        })
      });
    }).catch(function(error) {
      reject(error);
    });
  }
})

Am I assigning incorrectly a value or missing some conversion?

Answer 1

I found the issue, I was passing to:

gasPrice: w3.utils.toHex(transactionFee)

The whole fee: gas * gasPrice.That caused that internally my transaction fee was multiplied again by the gas.

I need to pass:

gasLimit: w3.utils.toHex(gas),
gasPrice: w3.utils.toHex(gasPrice)