Is it obligatory to pay expiation from savings allocated for transportation, books, and computer supplies, knowing that this is the only money available?

If breaking an oath does not involve an act of disobedience, then, according to some scholars like the Shafi'is, atonements (kaffarat) are not required to be paid immediately, especially if the money saved is needed for educational expenses and transportation. Therefore, there is no objection to delaying their payment until one is able to do so.

If you wish to atone by fasting now, that is permissible as long as you do not have money beyond what you need for your expenses due to your poverty. One who is unable to fulfill the three options (feeding, clothing, freeing a slave) should fast for three days. An 'unable' person is one who is eligible to receive zakat (definition), such as a poor person or a needy person; such a person atones by fasting. It is permissible for a poor student who is occupied with seeking knowledge to receive zakat funds instead of earning a living.