Getting the wei balance of a wallet using go-ethereum is easy! All you have to do is:

func etherToWei(eth *big.Float) *big.Int {
	truncInt, _ := eth.Int(nil)
	truncInt = new(big.Int).Mul(truncInt, big.NewInt(params.Ether))
	fracStr := strings.Split(fmt.Sprintf("%.18f", eth), ".")[1]
	fracStr += strings.Repeat("0", 18 - len(fracStr))
	fracInt, _ :=  new(big.Int).SetString(fracStr, 10)
	wei := new(big.Int).Add(truncInt, fracInt)
	return wei;
}

and then just use the result.

👨‍💻 /uno and /outside, @unofficial

actually it's way easier if you get the balance and new(big.Float).Quo(new(big.Float).SetInt(balance), new(big.Float).SetInt(big.NewInt(1e18)))