It would be the base price plus all the extras added on by the builder. This would include a lot premium, structural upgrades including the type of basement, wiring,extra outlets, etc. Also any upgrades to the interior such as flooring, carpeting, lighting fixtures, hardware, AC, kitchen and bathroom cabinets, counter tops, tile surrounds etc. It can get very expensive, it all depends on what was included in the base price. The models you walk through, are usually upgraded to the max! You should never go into a model home community without your Realtor. The person in the sales office is representing the builder, not you, and they are not required to be licensed in the state of CO.
It does not cost you anything to use a Realtor to represent you in your purchase or a new home or one that is being sold by an owner. A Realtor ( your buyer's agent) will provide you with advice and help you through the process. The builder pays the commission to the Realtor usually based on the base price of the home. The seller of a home pays both the listing broker and the selling broker. Do consider a Realtor to represent you in your efforts to find a home. It can be an overwhelming process and you don't want to over pay for any house!