OSTM efficiency building script

function Evaluate(a, b)
{
    return document.evaluate('//div[@id="' + a + '"]//*[@id="' + b + '"]/text()', document.documentElement, null, XPathResult.FIRST_ORDERED_NODE_TYPE, null).singleNodeValue.textContent;
}

function GetMed(a)
{
    return numberWithCommas(Evaluate(a, "cost")) / numberWithCommas(Evaluate(a, "description").substring(1));
}

function numberWithCommas(x) {
    return parseFloat(x.replace(new RegExp(',', 'g'), ''));
}

function MarkBest()
{
    var buildings = ["tent-building", "shack-building", "cabin-building", "cottage-building", "house-building", "manor-building", "dorm-building", "apartment-building", "condo-building"];
    var bestIndex = 0;
    for (i = 0; i < buildings.length; ++i) {
        var priceForOneGPS = document.getElementById(buildings[i] + "_gps-price");
        if (priceForOneGPS === null) {
            priceForOneGPS = document.createElement('div');
            priceForOneGPS.setAttribute("id", buildings[i] + "_gps-price");
        }

        priceForOneGPS.innerHTML = GetMed(buildings[i]);
        document.getElementById(buildings[i]).appendChild(priceForOneGPS);

        document.getElementById(buildings[i]).style.color = "red";
        if (i == 0) {
            bestIndex = i;
        }
        else {
            if (GetMed(buildings[i]) < GetMed(buildings[bestIndex])) {
                bestIndex = i;
            }
        }
    }
    document.getElementById(buildings[bestIndex]).style.color = "green";
}
MarkBest();