$500 might get you a used Juki 98Q -- which is an awesome machine.
Some shops will let you use their longarms if you take their class. Here, it's $75 for the class, then $75 to use the machine for the whole day. Just a thought...
Or, get the walking foot for your Bernette, and do walking foot quilting instead of free-motion. I do my best quilting with my walking foot.