Craigslist, ebay, off the side of the road...
You can find the best cheap mobility scooters at www.mobility-advisor.com/cheap-mobility-scooters.html. Another good site is www.scooter.com/ Most mobility scooters are comparably priced. And in most cases you can have the cost partially covered by medicare if you qualify.
You may be able to find cheap mobility scooters in New York if you visit several thrift stores. Some websites may help you find one, and maybe even help you get one for free.
Razor has about the cheapest, from 50$ to 130$-ish, but the best scooters are Phoenix, MADD gear, and district, but they're pretty expensive.
You can visit pridemobility.com to buy cheap mobility scooters since the site usually offeres discounts.
Medical scooters are available from a number of specialist online retailers including Discount Mobility Direct, Betterlife and Value Mobility. There are also many listings for used medical scooters on eBay.
FSP scooters
You can find Lime scooters in Los Angeles by using the Lime app to locate nearby scooters available for rent.
i bought mine at lucky scooters
Rawk.com but its in euro not in American dollars
You can purchase cheap mopeds from the following sources: Scooter, Mopeds, eBay, Power Sports Max, Auto Trader, Vespa Scooters, Piaggo Scooters, Argos, to name a few.
Amazon is a great source to locate cheap mobility scooters, such as the lark. They provide very competitive prices as well as detailed write ups on the various options that you can get, such as the vital cupholder.
Check local medical supply stores. It should be cheaper as you wont have to pay shipping. Otherwise try www.mobility-advisor.com