I have been down this road
The problems I encountered were:-
The staff can't speak English very well, so you can't be understood
One chap thought I wanted to buy a vindaloo, when I actually wanted to be shown how to cook it
I did end up buying one (but it was very good)
They tell you how to make a "very nice curry" at home, but its "homestyle"
They don't want to be paid for this information, and are slightly insulted
Also ,and probably most important, noone except us lot ever attempt it
They don't use curry gravy at home and don't understand the problems you get
One of the best things I did was go to Bengal Cuisine in London
http://www.bengalcuisine.net/default1.php?id=4It cost twenty five pounds for the lesson, but at least you were sure you were going to definitely be shown something
I've been let down loads of times because chef was too busy
But in answer to your question, I think it's easily worth 100 pounds for a full demo.
Learn how to make a full size curry gravy base
Learn how to precook meat, chicken and veg
Learn what spices are used and how to blend ginger/garlic (if used)
Learn to cook the final curry