Hi...i grind my teeth. my dentist says he needs to "fill" them at a cost of 1200...does this sound right?

Treatment plan: Need to clinically evaluate and see all radiographs and study models. Perhaps your dentist feels that you may need a full mouth rehabilitation due to grinding, or the dentist may selectively want to build up your worn teeth. Get a written treatment plan to evaluate what is proposed to treat your dentition.

Grinding: Generally grinding can badly wear teeth down, aging them prematurely. Your Dentist is probably right. If you are not sure, seek a second opinion (expect to pay for it), and take your x-Rays with you. Your question really can't be answered without a clinical examination and x-Rays.