You can auction them off on eBay. You will likely get what they are worth (and perhaps a little more) if you start at a fairly low price, and have pretty close to actual cost shipping. However, on eBay you do not control the price, the bidders do. If you have too high a starting price and/or reserve, folks don't bid. Figure about 10-15% for eBay and PayPal fees - percentage is less as price goes up. The top price you are likely to get is effectively capped by dealers offering the same item at a "Buy it now" price. Good picture(s) and accurate description of item and condition are essential to getting a good price on eBay. Original boxes and paper work increase the value. Because of shipping costs, selling cars or train set quality locomotives individually is not very productive - you'll need to group these. Good quality locomotives such as Atlas or Kato in excellent condition will normally get at least 75% of their original cost.
Hope this helps.