Book Publishing Co. wants to Publish my book what next?

The company sent me a letter in the mail telling me they saw my copywrite and they may be interested in publishing the mcript. After reviewing it they said they were interested in publishing it but I need to pay $11,200 total in 3 installments. Is this normal? Can I use their offer maybe as a bargaining tool to obtain the money? Should I just go to a lawyer? But any feedback would be appreciated. Thanks!