Mark, you don't mention your age but you do say you have disabilities. Can you expound on that?
Can you do repairs yourself? Can you get on the roof to caulk it? Can you service the engine?
Off the top of my head and that you mention that you are short on cash, I would think a truck and travel trailer would work best. First, the cost of maintenance on a regular truck would be cheaper.
Slides in an older unit would probably not be the best idea. A non-slide unit is cheaper and obviously an item that will not need maintenance. I've seen non-slide units that are pretty roomy inside. The slide mechanisms do take up space. A non-slide unit will have the storage cabinets that go all the way to the ceiling which will make it feel more spacious.
Not to get personal, but having an idea of what you have to live on will help giving you better info. If you have $1,500 a month to live on and you are paying for an RV, you won't have much left.
It can be hard finding free places to stay. Walmart will not want you for a week. Nobody wants to be so short of money, RVing will not be fun with no cash.
Be safe, take care,
Mark