If you don't care about the fancy stitches, look at the Brother PQ1500-S. New it is around $700 so a used one should be in your price range. It has a 9 inch throat. I'm currently quilting a 95 x100 quilt on mine. I'm only doing straight lines because I stink at FMQ, but I'm having no problem with throat space.
It came with a 1/4 foot, FMQ foot and a walking foot. It also has the extension table.
I bought it because it was the cheapest machine with the largest throat I could find. I had a cheap Brother for years and loved it. I kept it for fancy stitches.