Hardly any US aid to Ukraine is money. Mostly the amounts you see is the value of the aid.
The US sends Ukraine weapons and munitions that come from their own stock, and buy new ones for the US
Older munitions that are closing on their expiration date get used instead of the US paying for refurbishment.
Phased out hardware is donated as aid or lend/lease meaning the US buys the equipment they do want instead.
Limited amount of new stuff is donated
The actual money is then spent by the US, on replacement equipment. (This is purchased from US contractors who manufacture the equipment in the US and Pay Americans their salary).