Welcome to the hobby…I hope. $150, as Chuck suggests, will not go very far. At one time, perhaps 18 months ago, Bachmann Industries was selling a train set that had a very basic DCC set in it, complete with track and a locomotive with a decoder for the DCC operational system (DCC stands for Digital Command & Control). I don’t know if such an animal still exists, but if so, that will be your best bet, all things considered. At least it well get you in the door.
Otherwise, a good locomotive that is ready to run out of the box will be near $60 discounted or won on ebay. If you want the newer DCC operational control, then we are talking over $90 in most cases. If you get stung by the sound bug and want an engine that makes realistic noises, add another $50 at least, and that will be heavily discounted.
You also need tracks. What kind? There is snap-together track ($$, and limiting in the configurations you can make, plus those turnouts don’t work all that well without lots of fiddling), or there is flexible track that comes in three-foot lengths that you must bend to conform to your plan, and then glue or nail it into position to keep it from squirming back to tangent track (straight). Much less costly, but lots more work to get it ballasted and looking good.
This hobby is about money to an extent, although you are the determinant as to how much money. Otherwise, it is about determination and time invested. If you want to be happiest about your experience, doing a lot of reading and asking questions before you pick up a tool or plunk down the plastic is definitely the way to go. Otherwise it will be very expensive and most frustrating.
If you want some scenery, such as tunnels or hills, villages, streets and sidewalks, track signals, lighting, lots of trees, period automobiles, little people, here is where the money can get serious. The scenery and details can add up very quickly.
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