Why did X-Ray ask Armpit for an extra $30?

After X-Ray and Armpit buy their tickets (six each, which aren't as good as X-Ray planned they'd be), the guys talk to Felix, who tries to convince them to sell them their tickets at a good price, his arguments triggering, for Armpit, sudden insight into the economic process. X-Ray refuses Felix's offer, convinced that he and Armpit will be fine on their own. Later, while dropping Armpit off at school, X-Ray asks for more money to put an ad in the paper to publicize the availability of the tickets.