I started out drinking ruby port in my 20s but have really migrated to tawny over the last [cough cough] years. With the oxidation, an open bottle of tawny lasts basically forever, just like Madeira. I always try to keep a bottle of Sandeman 20 around as my house port. It's not Manton-level cheap...maybe $35 IIRC...but since I'm usually the only one drinking it, it lasts me for weeks.
LB: Cuvée Constance is