I see MTH Prototype Test Paint shells on ebay and I wonder if they're a good buy? Could you add wheels and couplers easily and have inexpensive cars for your layout?
Here are some examples:http://www.ebay.com/sch/i.html?_from=R40&_trksid=m570.l2736&_nkw=MTH+Prototype+Test+Paint+shells+O+Gauge