I have a HQ16 on a frame that I love. I bought it used and have never had a problem with it. My DH cleans it for me every 2 years; it was clean as a whistle inside after 2 years of use. It hasn't needed any other servicing yet. It gives me about 11 inches of quilting space on a smaller quilt, between 8 - 10 on a larger quilt.
Price-wise, used is always cheaper than new. The good news is that most quilters take care of their machines, so the used ones are generally reliable. Even so, you probably want to see the machine in person and run it on a quilt sandwich for a bit. I'll suggest finding a place where you can rent time on a long arm, so you know what to expect/look for during your shopping experience.
Other less expensive brands you can look at: Bailey's home quilter, New Joy Crystal Quilter.
I've never used either of those machines, but they seem to be pretty basic. There is a forum for the Bailey on yahoo, but I don't know if there is one for the New Joy.
Happy hunting!