For some reason, Viking named their mega quilters the same for their 9" and 18" machines so you need to figure out which one it is. The 18" inch one is made by Tin Lizzie and is identical to the TL 18SL. I have this one on the inspira frame and like it very much.
$750 is a good price for a used 9" one, expect to pay thousands for the 18" version.