The best way to go about this is to take the specs from your houseplan (if you don't have one yet, purchase a prefab home plan that closesly matches your dreamhome elements), and run them through a good piece of cost estimating software. Then you will see what the contractor is getting the materials for and how much markup he's slapping on. You will also be able to calculate approximate labor costs for each element of construction.
there's a good page that walks you through the process at http://contractorcity.com/main/articles/1/how-much-to-build-
Good luck and congratulations on building your new home! :)
Since you are not including the price of the lot, you might ask to get a materials list from each of the builders to see where the specific differences are, which will also allow you to be in more control of the choices you make. Just make sure that the builders are comparing apples to apples and look for specifics.
Another way to get an idea of what is reasonable is to look at homes sold recently (not foreclosures or short sales) new construction, make a reasonable deduction for the lot they are sitting on (location) and look at what the price per sq ft is running for already constructed homes.
Just a couple of suggestions,
Myke Triebold, GRI, SFR, ABR, LMC
Lisa makes a great point. When you are bidding the process let them know they have competition. Also, ask for reference and I would do a credit check. There are a lot of small builders that may not have the resources to complete the project. Look at there work that is completed and a few years old to check the quality, look at the job sites of current projects - it will tell you a great deal about their workmanship and company overall.
That is a great question. Having spent many years working for builders I can tell you the price will vary based on where you are building and also what you want to build. I see in your question that you said you are having the builder design the home. Keep in mind that each builder will build different and have different specifications for items you can see and also those that you cannot see (inside the walls). There is a whole range of building materials from which to choose from the strength of the concrete in the foundation all the way to the light fixtures in the home. Your best bet is to first come up with a design and set of specifications from which all builders can bid so you are comparing apples to apples. It may pay you to pick an architect or purchase a set of plans and specs before going to the bid process. If I can help in any other way please let me know. My number is 727-244-3664.