The money is only being spent on replacing the outdated military hardware that’s being sent over to Ukraine, which would otherwise be sitting and rotting in storage and would need replacement or expensive repairs to get running again. The US loses nothing from sending weaponry to Ukraine, and has everything to gain. It prevents continued Russian aggression on other countries (and Russia has explicit plans to invade more countries), saves Ukrainian lives and drives away the invaders so civilians aren’t being murdered in their homes, and boosts the economy through the increased number of jobs created for building the newer, better replacement equipment.
To claim that the money is being wasted is naive and misinformed at best, and actively disingenuous and malicious at worst. Putin would love for the US to stop sending support so he can continue his genocide.