Raechel, it is clear that you do not have professional representation in your effort to purchase this home and that is unfortunate as a good agent could help you understand how to determine the value of a home. Attempting to buy a house based on price per square foot is not the way you should be doing it as each house is uniquely different. Put another way, you don't pay for a car based on how much it weighs, instead you compare features, warranty, future value, make, model and a whole lot more before determining if it's the car for you. You should use price per square foot only as one tool to be used to help guide you in determining value. Regardless of what I or any other agent would tell you about average price per square foot in Saint Peters or Harvest Point it should not be enough to write a contract.
Contact a professional in your area and they will be happy to help or contact me and I will help you myself or refer you to a knowledgeable agent in Saint Charles County. You may save a lot of money using a local agent. Good Luck!!