Transportation only? $30 is probably a fair deal, but that will probably quickly turn into about $100 or so. The parts are ancient, and any upgrade would cost more than the initial outlay. You want to check all the cables for rust, and make sure the brakes and shifters work properly. The tires should hold air and not have copious cracking. It would probably need the attention of a bike shop, which can run as little as $25 or so up to whatever they charge these days for a tune-up.