one thing to consider is the amount of space you will have to turn your ordinary machine into a long arm.
If the space is only 9", you don't have much space when the quilt is rolled up. If you have ony 9" and the quilt rolls and takes up 5" then you only have 4" area for quilting. Be sure and see them in action before buying. You may want to consider an inexpensive commericial type machine to give you enough space.