Nobody gives the police this money. The police take the money from people they arrest. It is called asset forfeiture, it is legal, and it is widely used by police departments to pay for all that expensive military equipment they use.
"Why is the police becoming para-military?"
To gain more power over the population, to arrest more people, and to funnel more money to the well-connected corporations that benefit from this sort of tyranny.
Becoming? In the 1990s, when I was in college, state and local police recruitment information overtly described the organizations as paramilitary. Armed police forces are inherently paramilitary organizations, and always have been.
They're getting another influx of military equipment and personnel with combat experience (and expectations shaped by that experience) because the US military is gearing down after a over decade of greater-than-usual war.
The Army does, and then gives it to the sheriff's department when they're done with them.
Again - why? Why is the police becoming para-military? Do they fear another major protest and want to respond in force? What's the motivation behind all this.