Hi Deborah,
You have a couple of options.
To qualify for the rentista residency class, you must have an income of $2,500 a month or deposit $60,000 in the bank. That’s required every two years.
If your partner has $1,000 or more coming in from SS and/or his pension he would quality for the pensionado residency. If you were married that would also allow you to get pensionado residency. I don’t believe you can be listed as a dependent unless you are married.
A great resource for residency questions is Costa Rican attorney Roger Petersen: http://www.plawcr.com/
As far as transportation in Costa Rica, there are great public buses and cheap taxis. Scooters are also widely available but whether or not they would be practical depends on the area and your lifestyle. In some areas, like rural/country regions, a car is pretty much a must have.
Hope that helps and let me know if you have further questions.
Jason