Texas contract law, dispute with contractors

My house was recently damaged in Hurricane Ike and we need a new roof. We signed up on the blue roof program and called several roofers and a month after Ike we still did not have a tarp on our roof. Finally, a company came and tarped our house for a steep $800 and my husband thought that he was signing the invoice for the tarp. Well, it was actually a contract saying that we will use them for the whole rood job. The salesman was very slick and told my husband when collecting the money he needed to sign this form. My husband of course had enough on his mind and just signed. Anyway, I asked for an estimate and they wouldnt give me one and then gave our insurance company a bid for $12 grand-which other roofers gave me a bid for anywhere from 7-10 grand. My question is-Is this contract really valid and our we legally bound to use this sheister roofing company or can we go with someone else> the contract even states that if we go with someone else we will owe $20% of the 12 grand as a cancel fee. Your advice is much apprectiated.