Thinking of La Bec Fin in Philadelphia for my 50th birthday. How much should I plan to spend?

My 50th birthday is in the not too distant future, and I want to do something special to celebrate. Mom is 80 and for once I want to treat her, so I am thinking of taking her and my two sons via limo to La Bec Fin in Philly (I live in Hershey, PA), I have never had the pleasure of eating there and I am thinking about $600 for dinner for 4 does this sound about right or too low an estimate?