The machine you are looking at is not a longarm. It does have a longer arm than many DSM's, however. If it's possible for you to change the title of your post it might get more answers. I'm sorry I don't have any experience with the Juki TL-98Q Mechanical Sewing Machine.
Edit - I just read Leah Day's post, and apparently she is using the Juki TL-98Q for quilting, so it must be pretty good!
Edited again - I use the Bernina 440QE for piecing and used it for quilting until I got a longarm. It does offer the advantage of the stitch regulator (the only DSM to have one) and I thought that was a great option, but the price tag is beyond your budget. You might see if a used one is available, since I understand the 440 line is being discontinued.