JSFiddle - React, Tailwind, and code Playground

HTML

<form>
	<input type="checkbox" value="2000">
	<input type="checkbox" value="1000">
	<input type="checkbox" value="200">
	<input type="checkbox" value="600">
</form>

<div id="full-price" class="testFix">2000</div>

<script>

var form = document.querySelector('form');
div = document.querySelector('div');
price = +div.innerHTML;

form.onclick = (event) => {
	if (event.target.checked) {
		price += +event.target.value;
		div.innerHTML = price;	
	} else {
		price -= +event.target.value;
		div.innerHTML = price;
	}
}

</script>