I have an 820 and the throat is about 12" (not 18). I liked the frame, but don't want to tie up the 820 and have to piece on my older machine so I got a used long arm. I only paid about $800 (including wood frame). If I LOVE long arming and am any good at it, I can upgrade in the future. That Bernina frame is really nice, though. But the Tin Lizzie on the wood frame moved just as smoothly to me.
I only plan to do free motion and pantagraphs though. No computer and probably no ruler work.