If the house is designated "Historical" the value could be very high. You will want to hire a local Realtor that can do a market analysis and tell you how much to offer. I don't know if you have this where you are but may be one that has a "Historical Home Specialist" designation. No matter how much you are willing to pay, if you are financing it, it will need to appraise for that amount anyway. WIll be happy to find you a local Realtor if you want.