Who picks you up matters as much as where they take you. There are two primary business models for ambulance services in America:
Public/Municipal (911 Fire)
Many 911 systems are run by the local Fire Department. Because your tax dollars already pay for the station and the trucks, their billing is often "budget-neutral." Many offer a Resident Discount, where the out-of-pocket cost is waived if you live in that city.
In a public model, the primary goal is Public Safety. Any "profit" generated from billing is usually reinvested into buying new fire engines or training new EMTs. Because these agencies are governed by city councils, their pricing is subject to public hearings and local political oversight.
Private For-Profit
In many areas, the city "contracts out" its 911 services to a private company. These companies operate on a profit motive. They do not receive your tax dollars, so they must make 100% of their revenue from billing patients and insurance companies. This leads to higher "Sticker Prices" and more aggressive collection tactics.
Recent years have seen a massive trend of Private Equity consolidation in the EMS industry. Large national conglomerates now own many local ambulance brands, often focusing on "billing optimization" which can mean higher costs and less flexibility for the patient when it comes to financial assistance programs.