There are many ways to look for a used RV,don't be in a hurry do a lot of research, Kick some tires,decide which floor plan you can live with.
I have to agree with the others here that renting first to get a real feel and the experience of RVing,that way you will know if you will enjoy the RV Lifestyle.
One of the many avenues to look at is the
Former Rental MarketThere you will get a good value for your money and a RV that has had proper maintenance.There are 100 owners on that thread and all are happy with their choice.
Enjoy your quest for that perfect RV that will suit your needs and budget.