Keep the XD9, add the Taurus PT1911 for $500 or so new (shop around), then, once you are hopelessly hooked on 1911s, you'll find a used Colt 1911 in great condition for $600-700 or thereabouts. Now you are in deep!
Re trade-ins versus selling on consignment versus selling person-to-person, say a certain gun is valued at $450 used in 98% condition. The gun shop might give you $250 in trade-in. Put it up for consignment at the same shop, you set your asking price and your (hidden) bottom price. The shop gets the best price they can, acting as your agent, and then takes 20% of the actual selling price. If your $450 value gun sells for $400 on consignment, you'll get $320. If you sell person-to-person, you have a chance at getting the $450 the gun is really worth.