Are you asking about a new machine, or used? I am planning to begin learning to do free-motion quilting myself, but it is my understanding that any machine will work with the right foot. Even if your feed dogs don't drop, you can cover them. The old singers had feed dog covers to use when darning, using the buttonhole attachment, or free-motion quilting.
The machine I plan to use for learning about free motion quilting is a Singer 301. Fortunately, this one has feed dogs which do drop. I got this machine at a yard sale, and it's a great machine.