const obj = {
    'reno': '$15000',
    'audi': '$20000',
    'bmw': '$30000',
    'peogeot': '18000$'
}
const s = Object.values(obj).reduce((val, el) => val += value(el), 0)
alert(s)
// Вернет число
function value(str) {
	const i = str.indexOf('$')
	if (i === -1) return +str
	return +(i ? str.substring(0, i) : str.substring(1))
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/collect.js/4.34.0/collect.min.js"></script>
    <script>
        const objCars = {
            'reno': '$15000',
            'audi': '$20000',
            'bmw': '$30000',
            'peogeot': '18000$'
        }

        const total = collect(objCars).sum(value => value.replace(/\D+/g, ''));
        alert(total);
    </script>