var total = 0;

function updateTotals(id) {
	var camp = 'camp' + id;

	if(document.getElementById(camp).checked) {
		total++;
	} else if(document.getElementById(camp).checked == false && total != 0) {
		total--;
	}
	
	document.getElementById('cost').innerHTML = 'Total Cost: $' + 2299*total;
}