They don't have to fund everything themselves. The armored vehicles, assault rifles, body armor and bayonets they got from the Defense Department were free.
They were only free
on the condition that they find some way to use them within one year.
Otherwise, the Federal Government may take the equipment back to give to another local law enforcement agency elsewhere.
That is the kind of cost-saving measure that the US Congress considers appropriate.
(Cutting production of such equipment down to the levels that the military leaders actually request would be crazy, as military contractors constantly remind them that they run factories in almost every congressional district and cutting production would mean downsizing and lead to unemployment among the congressman's constituents.)
That is why you see MRAPs showing up in the middle of the night at the doorsteps of houses where the cops suspect that a teen could be selling weed out. If they didn't use them then, they could loose the thing before the back robberies and terrorists attacks that could happen decades later.
The vehicles do so much damage to the roadways that using them frivolously costs local governments more than the vehicles are worth, but that doesn't matter because infrastructure spending does not come out of funds earmarked for the police department.
If the Feds don't give them and let them keep the toys they want for free, then they have to fund them through Civil Asset Forfeiture.
(Of course, since that funding is less predictable some police chiefs opt not to use those funds on any "must have"s, instead allocating those funds for "like to have"s such as a new margarita machine for the office.)
A lot of cops like to let drug dealers and gun runners pass through unmolested while they are carrying their contraband, so that they can catch them when they are coming back with cash. It is more convenient to sue a pile of money than a pile of stuff that they could not legally sell off for money.
Congress is not the best at predicting unintended consequences of measures meant to help cops fight the drug wars.