Should I wait until I possess sufficient money to pay the expiation for an oath, given that I fasted three days for each oath because I was unaware of the priority of payment, and my current available money is my school allowance?

Expiation by fasting is only valid for those who are unable to perform the three options for expiation: feeding ten poor people, clothing them, or freeing a slave. Whoever cannot find any of these three options then resorts to fasting for three days.

If you were able to feed ten poor people at the time of breaking the oath, then your fasting is not sufficient for expiation.

If you are now unable to feed them, then the two expiations remain your responsibility until you find what to feed them with, and fasting will not suffice for you, because you were financially able when you broke the oath. This is the view of the Shafi’i and Hanbali schools.

As for the Hanafis and Malikis, they hold that what matters is the time of performance, so your fasting is now sufficient due to your inability to feed them.

The most cautious approach is that you fast for the expiation, then if you find yourself financially able, perform the expiation by feeding or other of the options given.