It depends what you wish to get out of the day. Do you want to learn how to take a photograph of a bird in flight for example, the techniques etc or do you wish to learn more about the animal you wish to photograph and its environment?
In my opinion if you choose to go on a group workshop at a falconry day or similar 'set up' type of workshop you are paying for the shots being setup for you so you go home with a great set of close up images of birds flying from post to trainer etc very close to the photographers. You will never get that close to in real life and you will be a bunch of other photographers who will have the same shots as you. However this will probably not help you take wildlife photos for yourself in the wild. However if that is what you want then this is a great way to get 'the shot'. Just don't kid yourself (or others) it is wildlife.
Better in my opinion to go with somebody who will show you how to photograph 'real' wildlife in a small group of no more then 2 or preferably one to one, witness some real wildlife in nature and 'hopefully' get some good shots. Remember real wildlife is just that 'wild' so there are no gaurantees.
Regarding value for money well it depends what you expect for £100, if there are 5 on the course and the workshop leader has to pay for a falconer, access to a falconry centre, thier own transport etc then I would say that is a very fair price.
On a one to one basis then £300 is a very good and fair price.
There are many to choose from, but I have used Craig Jones, who has his own unique style and is very ethical about his work. You will get a very long day and some real wildlife photography opportunities and learn plenty from him while you are at it. You could do worse than try his Norfolk Spring Tides workshop or one to one.
http://www.craigjoneswildlifephotography.co.uk/workshops/spring-tides-and-barn-owls.php