Yes it is expensive, but at least you get the feeling you get something worth your money. We were 2 adults & 1 child and wanted also to see St. Pauls before the tower. Seeing the excredible entry fee for that we simply skipped St. Pauls. It's a church : even though it is impressive and I remember the whisper gallery from an earlier visit, it is really not worth the price. The tower is, you visit the most important historical buildings in the city with vastly recorded history. It's worth it.

Tip : close by the undergound exit there is a souvenir shop that also sells tickets, forget the official ticket booth with the long queues, this is faster with no extra charge.