I think 1. is the least likely. There are clearly some instances where Ukraine is using its own money to procure some weapon systems on the open market. Even so, UA is not a wealthy country by any standards (both nominal and PPP per-capita GDP are about half of Russia's, which are about half of OECD average). Given that much of its economy is in tatters, it isn't in the position to enrich arms dealers with high markups. Direct cash aid provided by the US and others is earmarked for soldier salaries, administrative costs for the gov't, and humanitarian relief. I don't think the UA gov't is being given a large lump of cash to "buy overpriced weapons". In cases like Germany where the gov't says: "Here is a menu, pick what is useful to you", it is possible that the German gov't will pay a premium to its domestic manufacturers to supply new weapons, but that seems unlikely, since those mfrs want to maintain a good relationship with the hand that feeds them.
I believe the majority of weapons transfers are gratis, with the understanding that the original owners would like to use these weapons themselves, in exactly the kind of conflict Ukraine currently finds themselves, but are happy to let UA field them and actually pull the trigger. This is pretty much the best possible scenario for the donor nations, as they are not putting their own forces at risk, they are degrading a threatening rival military, and they get to assess the effectiveness of their weapons systems under the most realistic conditions possible.
Most NATO countries have not fought a peer nation. So although the performance of their military hardware has been tested in Iraq, Afghanistan, Syria, and other conflict zones, the belligerents have often been quite asymmetrical in their capabilities. Up until February 24, 2022, Russia's Armed Forces were considered a peer force for any other military in the world. Seeing your weapon systems in action against such an adversary is the ultimate test of its capabilities, and gives you some idea how an actual conflict against that adversary (or similarly armed adversaries) would play out. It would not be economically or strategically irrational for NATO and allied nations to pay UA to deploy their weapons systems on the front lines for these reasons.
Turkey has surely gained the most PR value for its Bayraktar line, and has already lined up eager buyers based on its performance in UA. But there's no mistake that virtually every modern anti-tank weapon on the market has also seen a huge boost due to the massive number of burned-out T-72s on the fields of Ukraine. Even the Carl Gustav took out a T-90M recently, to say nothing of the NLAW, Javelin, Panzerfaust, Stugna, etc. ad infinitum.