So far almost all weaponry has been either directly donated or was bought by Ukraine, but refinanced by funds from the EU or US. Some small stuff was likely directly bought by Ukraine (think of all the COTS drones they repurposed for dropping grenades etc), possibly also ammunition and small weapons, especially if it came from countries who are not really supporting Ukraine (think of Iranian artillery ammo that somehow appeared in Ukraine possession), but that isn't the biggest share of the costs for the war. The financial part of the actual war is so far pretty straightforward - Ukraine fight, the West provides weapons to do that. It is much more a political or military decision what is provided than a financial question.
Rebuilding the country and covering the ongoing costs due to the destruction, loss of workers due to having to fight or having left the country etc is a different and more complicated topic and one area where Ukraine definitely will struggle, unless a massive programme will be created, similar to the Marshall plan after WW2.