Old exterior door won't seal right, cold air pouring in

Bought the house last year and the front door has been driving me nuts since winter hit. It's an old wooden one with a storm door in front, and no matter how much weather stripping I add it still whistles. Tried the foam tape stuff from the hardware store and it helped a little but not enough. Thinking about replacing the whole thing but not sure if I should go cheap fiberglass or save up for something nicer. Anyone dealt with this on an older home? Tips on measuring for a new one or other quick fixes would be huge.