My personal scooter weighs 35 pounds assembled, folds down into a bag the size of a golf bag, and has a lithium-ion battery that will last all day for me at WDW (and I am a 3L: a Large Lovely Lady).
However, it's price tag is off-putting for many; the average price shipped is about $2500. My family and I knew that it would become my legs - and I use it every day now - so we considered it an investment; it is made from aircraft grade aluminum and will probably outlast me. I can drop the handlebars, and put it assembled (with the brakes locked) in the back of my Kia Soul with one of the back seats folded down, and away I go.
There are all kinds of options out there - you have to prioritize what your most important feature is first, and then search for an
ECV that has that primary feature. (If it is price, then you won't need the contact info for my scooter manufacturer... LOL.)
The one thing I would caution against if buying a used rental unit is this: Until you know what the actual useful daily life of the battery is, either take along the charger, or consider buying a replacement battery (there are many sites - including
Amazon - that sell replacement batteries for
ECVs). Additionally, when looking at a used unit, if you see plastic body work that is cracked, damaged or missing, it could indicate that the unit was poorly treated; it may have been driven off a curb, hit by another vehicle or turned over in an accident. Never buy one without riding on it - if it makes weird noises (like a rhythmic "ticking" sound) or if it is missing chunks from the tires, that would also be a red flag for me.
Last but not least, if you find a unit locally, remember it will fly for free as medical equipment if you travel by air. Put out the word on NextDoor and Facebook to let folks in your neighborhood know that you are searching for a good, used ECV; you may be able to find a gently used bargain close to home!