There are many ways you can approach this situation.One thing, you can do is hire an experienced realtor like myself to put together a comparative marketing price analysis to determine fair market value and secondly you can hire an buyer's agent to represent you in finding the right price and place for you.
I would suggest the following, you can request to have an appraisal completed on the property and make the offer subject to the appraisal being acceptable to you and cap the dollar amount.
If you are working with a Realtor, they can provide you with a market annalysis, to determine fair market value. For further details you can reference my blog which is very detailed regarding the subject of negotiating an offer.
If you're looking for assistance with a purchase and how much to offer, you will need to hire a realtor who practices buyer representation to represent you rather than the seller. This way, they can work FOR you rather than merely WITH you. Good luck.
Century 21 Princeton Properties