Hi RRRose and welcome to Cruise Chat.
It's very difficult to assess the price of shore excursions in a vacuum like that. Depending on the excursion, prices can vary tremendously. I'm just off an Alaska cruise, where excursions in some ports varied from $35 for a short walking tour, to $495 per person for a dogsledding or flightseeing excursion.
On some of the more upscale cruise lines, some or most excursions are included in the price of the cruise, on many itineraries.
Excursions in some ports are more expensive than others, too. It's easy to find excursions costing an average of $100 in Alaska and Europe, but not in the Caribbean.
You can go onto the web sites of various cruise lines and see information for shore excursions, and see which ones you would be likely to buy, and add up the cost that way.
Also important in determining the value of an all-inclusive cruise line is how much you like to drink, both alcoholic and non-alcoholic beverages.