Russia is weak, but they are also a nuclear power with a weak leader that may lash out if cornered. There is a reason nuclear powers have never been in direct conflict.
If Poland is attacked by Russia, the US is going to war as well, since Poland is a NATO member. May sound callous but I would prefer Ukrainian troops make the sacrifice, then potentially risking US soldiers. While Russia is weak, in a direct conflict with US there will certainly be US casualties.
Regarding the amount of money given, a lot is to replenish our own stockpiles. Not to mention if $100B+ neuters Russia and diminishes there capabilities to the point they are no longer threat, then it's money well spent.