Check out the Juki Yahoo Group. I've heard them talking about "stretching" the Juki to a larger throat. I guess there is a company out there that does it. I think it was north of $1000 for the conversion.
I had the Juki TL98QE on a stretch Hinterberg frame. Got the stretch because I thought I would upgrade to the Voyager later. It lasted 6 months before I got annoyed with the lack of throat space. I did a Queen on it, but it was very frustrating, couldn't do a 6" block at once when it was all rolled up. The largest pantograph I could do was 4" maybe.
I made the jump to a 24" Prodigy longarm. Don't know how I did without it!
Also, check out Longarm University. www.longarmuniversity.com. They have a for sale section. There are used longarm as well as used home systems that might fit in your budget.
Good Luck!