HD is probably going to be your cheapest option. Ask if they can order it at the contractor desk. I think the ones my coworkers bought there were $38 or something.
If you decide to buy online, try searching google shopping for "Gott Cooler" (if you sort by price you'll have to go several pages in to find the cheapest one, I don't know if the link will work, but here
)they're made by rubbermade but they're a little less expensive and they have a dispenser opening that will accept a 1/2" nipple without modification.