Confirm you are talking in £ and not € and includes the VAT @ 10%
I am not sure what you mean by drink package.
Do you mean that the £ 30 is for the 3 course menu, with a variety of options (fish or meat) for the main course, and the £ 20 for wine during the meal and spirits and drinks consumed afterwards, and possibly before ?
If so, personally I don’t find that overpriced.
The setting is one of the best in the Port, in my experience the food and service has always been top notch, although others may disagree, and they have their own free parking right outside the front door.
I’ve never seen a buffet being served there, and quite frankly I doubt that it would be very much cheaper as the kitchen would have to factor in the cost of the unconsumed food and they would still need staff to remove cutlery and tableware.
Maybe you could ask each guest to donate £ 10 towards the bar bill ?