The answer to this is actually rather simple.
The problem is not the amount we are spending, as much as the how it is being spent.
Most of our military equipment is old. As in 3 decades old and older old. It is quite common to see equipment like trucks and the like in the motor pool that were new during my first enlistment in the military.
In 1985.
A great percentage of our equipment is to be honest falling apart. We are spending huge amounts of money in refurbishing and repairing them, something that no sane organization anywhere else does that. Does anybody think that FedEx or UPS uses 30 year old trucks to deliver packages? Flies them around in 30 year old planes? But that is exactly what the US military does on a daily basis. Trucking companies know that after around 10 years the maintenance costs and down time start to outweigh any benefits of having a "paid off truck", so they replace them.
The military does not do that, because then somebody would jump up and down and scream that we were "wasting money".
Then there is the other thing. 1/3 of the DoD personnel are civilians. Then you have the contractors, which are hard to figure out buy many estimate that the number is the same or higher than the members in uniform (as many as 1.5 million).
So first step, get rid of most of those contractors. Doing jobs such as washing dishes, changing light bulbs, guarding the gates, mowing the grass, managing the barracks, issuing the equipment, changing the oil in vehicles, and 10,000 other jobs that the military itself did just fine until the 1990's. Fire most of them, put the military back to work doing those things.
The same with the bloated civilian sector of the DoD. The number of civilians I see today is staggering to somebody who served in the 1980's. And these are government employees, handling such important jobs as checking the ID of people entering the gym, and running the projector at the base theater. Get rid of them all, that is a job that formerly was done by military members who were in the last weeks-month of their contract and were coasting before getting out, somebody who was injured and could only handle such light duties, or as a "bennie" for somebody who had been working their butt off on a difficult mission and a few months of easy duty was part of the reward.
Nope, not no more. Now they are all done by civilians. Cut the fat in those areas (and start replacing the oldest equipment which will eliminate maintenance costs) and you will get a better and stronger military with little to no added expense.