Ever since I learned that the whole charity thing is added to get you to pay more, and not because the companies involved care about the charities, I've stopped feeling guilty for whatever amount I choose to pay.
And, yes, there is a huge moral different between paying even a tiny amount for a game and pirating it for free. You have their permission to do the former, but you do not have their permission to do the latter. And, ultimately, permission is the dividing ling between stealing and legitimate ownership. (If not, then gifts would be immoral.)
Finally, "personal use" by its very nature includes the ability to give it away. If I buy, say, a cup for my own personal use, am I restricted from giving it away to someone else?
It is a bit of a jerk move to buy games and then sell them, though. But that's more because you are depriving them of revenue and cheating your friends out of a deal. It's not because you don't have a right to sell your keys.
EDIT: realized I forgot to answer the question. I generally pay 1 cent at first, as it gives me more time to come up with the money. I then never pay more than the average until after the sale is concluded, so my payment will not make someone else have to pay more. In my opinion, we have an obligation to other buyers, too, not to artificially increase the amount they have to pay.
Ultimately, I generally just pay the minimum amount I need for what I want. Again, I'm wary of being manipulated. If I want to pay for a charity, I can pay the charity directly instead of increasing costs for everyone else.
Plus, the entire reason why I got into these bundles is that I have a very tiny gaming budget.
