However, don't confuse the military surplus program with a free lunch. These used military birds need work done to them in order to bring them up to law enforcement flight standards. For example, a mere makeover with your logo and agency color scheme involves stripping the paint, applying corrosion coating, priming, and painting, which can easily cost $30,000 or more depending on what type of corrosion they find. There was a news story in January of 2015, about the Newark (NJ) Police Department getting two free helicopters (one flyable, the other for parts) at a cost of two million dollars when everything was said and done. Free is a relative term. It was still cheaper than a new more modern helicopter.
Parts for military surplus aircraft usually end up pennies on the dollar compared to buying new parts off the shelf. For example, I obtained a part for one of my former helicopters on a transfer from another agency. The same part new would have cost my agency $10,000. Keep in mind that military surplus parts are subject to availability and become harder to find as time goes on. If you can't find it used, you may have to buy it as a new surplus part. Still, for the most part, military surplus tends to be very cost effective. Just remember that like anything else there is a learning curve to the process.
Another consideration is political. Military surplus has received a bad name now due to negative stories in the media about the militarization of police. Some agencies are shying away from military surplus altogether.
Model
After you identify the role, mission, and basic logistical factors, you are ready to pick your model of helicopter. There are numerous manufacturers, which include but are not limited to, Bell, Eurocopter, MD, Robinson, and Sikorsky.