Estimating contract execution price in ETH

[herocode-it]

Hello.
I'd like to send all available USDC tokens from my wallet to another address (basically sweep them).
My wallet only has USDC, no ETH - so to execute the transfer I need to send myself some ETH from another wallet, so I have funds to cover the gas.
I don't want to send too much, otherwise the unused ETH will be wasted.

I've read that I need to multiply gas times maxFee, so I try to estimate the fee using contract.estimateGas.transfer and then multiply it with feeData.maxFeePerGas, however the resulting value does not make sense.
For example: 48670 * 1500000020 = 73005000973400 (73005 Gwei), but I see on Etherscan that similar transaction sent at the same time used only 0.000655 Gwei. It seems that the gas estimate is okay, but the feeData.maxFeePerGas is way too big?

My code (I'm using goerli for testing)

const ethers = require('ethers')

(async () => {
    const provider = new ethers.providers.EtherscanProvider('goerli', 'ETHERSCAN_API_KEY')
    const wallet = new ethers.Wallet('WALLET_PRIVATE_KEY', provider)

    // USDC goerli testnet address and ABI
    const contract = new ethers.Contract(
        '0x07865c6E87B9F70255377e024ace6630C1Eaa37F',
        'USDC_ABI', // from: https://api.etherscan.io/api?module=contract&action=getabi&address=0xa2327a938febf5fec13bacfb16ae10ecbc4cbdcf&format=raw
        wallet
    )

    const tokenBalance = await contract.balanceOf(wallet.address)
    const feeData = await provider.getFeeData()
    const functionGasFees = await contract.estimateGas.transfer('RECEIVER_ADDRESS', tokenBalance)
    const txGasPrice = functionGasFees.mul(feeData.maxFeePerGas)

    console.log('functionGasFees: ' + functionGasFees.toNumber())
    console.log('maxFeePerGas: ' + feeData.maxFeePerGas.toNumber())
    console.log('maxPriorityFeePerGas: ' + feeData.maxPriorityFeePerGas.toNumber())
    console.log('txGasPrice: ' + txGasPrice.toNumber())
})();

Output:

functionGasFees: 48670
maxFeePerGas: 1500000020 // is that correct?
maxPriorityFeePerGas: 1500000000
txGasPrice: 73005000973400 // that's 73005 Gwei, while a similar transaction was under 1 Gwei

Can anyone tell me what I am doing wrong? Huge thanks.

[zemse]

Units of functionGasFees is gas. Units of maxFeePerGas (or gasPrice) is ETH / gas.

Hence multiplication of these two things will yield ETH.

const txEthAmount = functionGasFees.mul(feeData.maxFeePerGas) // not txGasPrice
console.log(formatEther(txEthAmount)); // 0.0000730050009734