I just got done "researching" the same questions.
What seems the easiest and least expensive way to purchase these (And I could be wrong, but I checked alot of different ways) was on hotwire. If you look for the tab that says savings club, you will find directions to sign up for 30 days free. If you cancel before the thirty days there is no charge. After 30 days seems to be $7.95 a month. Anyway, I plan to order my vouchers and cancel.
On the everything you wanted to know board I found that the quick and casual voucher was selling on hotwire for $11.00. That includes an entree, a side, a drink and dessert at many counter service restaurants. The way I figured it was that I could almost always get at least the $11 worth of food, maybe more if I ordered all the most expensive things.
There is also a lunch voucher for sit down restaurants for $31 and it includes appetizer, entree and dessert. I looked at quite a few menus and found that even ordering the most expensive stuff, I might come out $5 ahead. There was potential for coming up less. It does include tip & tax, but I figured that in.
I didn't really research the character breakfast voucher which I believe is $17. But. since it includes tax and tip, I think you would come out ahead.
It also seems that if you order carefully, you could use two or three vouchers for a family of four. We have ordered the 2 pizzas at the counter service and shared it between the four of us.
There are tons more details on the everything thread (pinned at the top of the board).
Good luck!