20-25% is about average for non-pension expenditures on police.
It's easy to lose context of just how massive a part of PA Philadelphia is. The city proper alone has more than 10% of the state's population (1.5MM to PA's ~12.7). Add in the other PA counties and you're close to 4. Add in the out-of-state parts of the Metropolitan area and you're quickly closing in on 6.
I've always felt safe when I've been there but given the sheer volume of people, I'd surprised they're not spending a larger amount of police forces.
When you stop and think about it, there is a near-constant state of emergency, and this no doubt applies to any major American metropolitan area. I'm not at all surprised that the police department has such a huge budget here.