the keywords are: industrial, walking foot, straight stitch, zigzap. I don't have any experience, but couple of people told me that normal household sewing machine
will do for most of the tasks (sails, perhaps not many layers of sunbrella) if you go slow. Also Beth Leonard & Evans Starzinger somewhere say that they always had only normal household sewing machine.
If you have spare 800 get the Sailrite
machine, which btw has a cheap
Chinese clone (though I forgot the name of it) or you can try ebay where you can find good deals on Pfaff, Singer, Consew and others.