The price a builder charges to build a home on your lot depends to a great degree on the finishes you want within the home. My recommendation would be to meet with a few different builders to have them bid the job on an apples-to-apples basis. But as important as cost is the relationship you have with the builder, as it will be likely at least a year long partnership, and is one that can be stressful. Working with a realtor can also give you another professional source to guide you through the process.
Call me for help with builder referrals, or with any other questions.