You, my friend, are in what is called a market called a monopolistic competition market type, meaning you are selling a product that only a handful of other producers sell, and that allows you to sell at a price above where marginal cost and average total cost meet, and rather should be sold above that point at the demand line in a process known as price discrimination.
To elaborate; you can sell at any price that the consumer is willing to pay for. Just make a post informing others that you are selling a 3 month code, and let them offer. Odds are they are looking because they desperately want one as quickly as possible, and will pay more for the sake of convenience.