My DH is an EMT for an all volunteer rescue squad. Their county charter only allows their squad to provide rescue, BLS, and transport, for more serious situations paramedics and/or life flight are dispatched as far as injuries and some illnesses. His squad handles all extractions, water rescues, and coordinates with the FD for HAZMAT.
On some weekdays the squad DH is affiliated with doesn't have enough coverage to operate BLS, and in that case ambulance BLS calls are handled through mutual aid by a neighboring squad with paid EMS or by paramedics through the local hospital. (They can always cover rescue, they have several members who are trained in rescue but are not EMT-B's who can respond to rescue calls around the clock.)
Now onto costs.
If the call comes in to DH's squad and the squad volunteers respond, there is no charge, be it for anything from bringing the rescue rig to provide additional support for the fire department to responding to a major MVA with extraction and transport to a kid who breaks his arm while skateboarding. When the squad is asked about billing or payment the person is told that there is no charge, although if they'd like to make a donation to the squad it will be gladly accepted.
If the squad isn't manned and the paid squad from the next town responds, that squad sends a bill for $250.
If the injury or illness is severe enough that ALS is warranted and the medics respond either via ambulance or life flight, a bill will be sent--the charge varies but life flight starts at $5000.
In most cases the patients insurance pays the bill, but DH knows of a few times when the paid crew responded to what was not an emergency but someone wanting a ride (yes, unfortunately that happens), and their insurance refused coverage.
When my son was injured while playing football (sprained arm and shoulder dislocation that "fixed itself"), we RMA'ed and transported him to the ER ourselves, and never got a bill, even though the local rescue squad had responded. We sent a donation, because we felt it was the right thing to do.
Anne