Procurement for Ukraine is done through Congressional appropriations and bought through our Foreign military sales program. Regular budgeting for FMS is not part of the standard military budget process. One also needs to understand that many of the weapon systems going to Ukraine and our foreign Allie’s are not the same top of the line equipment that our troops use. They get systems that are similar but often are slightly inferior to our standard equipment.
A good example of this was when Carl-Gustaf recoilless rifles Mark II were donated to Ukraine and they were replaced with Mark IV. Made of titanium instead of iron and 15 pounds lighter.