Quick and Casual vouchers cost members $11.50. Vacation Kingdom Lunch vouchers cost members $30.
How much should you pay on eBay? That depends.
If you have no desire to get a Connections membership, or go through the process of joining, ordering, and cancelling, vouchers from eBay could be an answer - depending on the circumstances.
I would only get Q&C vouchers via eBay if you plan on using them at Beaches and Cream or Pepper Market. By the time you add the final auction amount and the shipping, you are not likely to save any money at other counter service locations and would be better of just paying cash for your meal.
B&C and PM are a different story. You could feed a family of 4 with two vouchers. We often go to B&C and get $50+ worth of food for the two vouchers. We usually get the drinks, two double burgers with sides, and two huge sundaes. If you would definitely be going to B&C and ordering that much food, it might make sense to get these vouchers on eBay. After all, if you get $50 worth of food for two vouchers, every dollar below $50 you pay represents some amount of savings. How much would I pay? I guess $15 to $20 max including shipping might make them worth it to use at B&C.
Same with the Vacation Kingdom Lunch vouchers - how much they are worth depends on where you use them and what you order. Check out menus to see what makes sense. For instance, I will use one of these vouchers at the Rainforest Cafe. I'll probably get the stuffed lobster, a shrimp cocktail, a drink, and dessert. With tax and tip the bill for that would be about $70. Even if you paid $50 for the voucher you'd still be saving $20. If you ordered cheaper food you might not save anything.
Do your research. Decide where you would go. Look at the menus and decide what you would order. Figure out how much it would cost, decide how much you want to save, and then you will know how much to pay.