I think if you're going to have a 3 hour time, you should be able to tailor the class to the needs of the winner. If someone is learning color theory is a bit much for some people (I'm one, but I know how it works and I have dropped classes when they got too into it for me - that's just me). If you can have a couple of choices, this will be more of a draw to more people. You could make up a pillowcase (and a pillowcase kit), this would be able to show what you are bidding on and how it will look after the class. Or you could do the same with a set of two placemats (show a finished one and the kit for the other two), you can make one in class and they can go home and make the second one. These are the kinds of things I would offer, just remember you should be able to show a finished example at the auction (people like to see what they are bidding on). Good luck