I checked out the prices for the Stonehenge bus, and it's a spicy meatball. 79 GBP, so $140 Canadian. (64 pounds for the bus, and 15 for admission.)
A regular bus on its own (city to city) is 9 pounds, plus a taxi from the bus station to the terminal, so say 20 pounds.
A regular train is 42 GBP, so $76 CAD.
That's a hell of a difference. The train is half the price of the Stonehenge bus, and a lot faster. It comes down to two things: a) will the Stonehenge bus get us there on time for boarding, and b) do I want to pay the extra seventy bucks to see Stonehenge. Granted, the bus portion itself is 'only' 40 bucks, and admission the other thirty, but...
I have no problem shelling out while on vacation. Willingly being GOUGED is a different question.
With any luck, the Stonehenge bus won't get us there on time, making the whole question moot.