[MC-XOBAHCK]

Вот ещё такое решение:

<div>
    <input type="checkbox" name="price" value="170"/>
    <label>250г</label>
</div>
<div>
    <input type="checkbox" name="price" value="680"/>
    <label>1000г</label>
</div>
<div>
    <input type="checkbox" name="price" value="680"/>
    <label>1000г</label> 
</div>
<div>
    <input type="checkbox" name="price" value="680" />
    <label>1000г</label>
</div>

<hr>

<div>
    <span id="result">0</span> грн.
</div>

<script>
    let result = document.querySelector('#result');

    function sum() {    
        let checks = document.querySelectorAll('input[name="price"]:checked');
        let prices = [];
        let summa;

        if (checks.length > 0) {
            checks.forEach(el => prices.push(+el.value));
            summa = prices.reduce((acc, element) => acc + element);
        }
        else summa = 0;

        result.textContent = summa;
    }

    document.querySelectorAll('input[name="price"]').forEach(el => el.addEventListener('input', sum));
</script>