There are all different kinds of restrictions. Many agencies require you be a citizen, many are (in my area at least) are looking for people with military time or college, and some places want you to live there before applying. For example I wanted to be a Boston cop for a long time but they require you live in the city for at least one year before applying. All things to consider.
As far as pay goes it usually starts around 45-47K a year for probationary officers. But again, it depends on the agency.