This is my opinion and is not legal advice. You should always seek competent legal advice. That being said....
In order for a contract to be valid, there must be three elements: 1) the parties must be in agreement as to what constitutes an acceptable offer; 2) the agreement must be in writing and signed by all parties (verbal and unsigned agreements don't hold water in a court of law); and 3) something of value must be given in consideration (i.e., earnest money deposit). In Massachusetts, a signed Offer to Purchase by both parties can constitute a valid binding agreement, even if the Purchase and Sale Agreement is not yet signed.
However, given the scenario provided above, all you did was accept an offer by e-mail. But, it lacks an agreed upon price. So, if there is no price, how can you accept an offer? It appears that there is no agreement, there's nothing signed by either party, and nothing was given in consideration. Thus, I am of the opinion that you do not have a legally binding contract.
Again, seek competent legal advice.