My aunt who is disabled has a Drive Medical Spitfire Scout 4 mobility scooter and it's pretty lightweight and pretty well built.
You can buy the Drive Medical Spitfire Scout 4 mobility scooter for around $750.00 online which is a pretty good price for a mobility scooter as most of them cost more than that.
The lightest weight mobility scooter that I've seen online is the Smart Scoot mobility scooter but that one is over $2,000.00
But it could be well worth the cost as it's easy to travel with and very easy to load into a vehicle as well.
Some other good lightweight mobility scooters that have good reviews are the Active Care Spitfire and the Invacare Lynx L-4 as well as the Shoprider Sunrunner mobility scooter.