Getting the scale is not hard - just take a high resolution TIFF file and print it out on a plotter or other large media (as mentioned Kinko's can do this for you - or I could on our plotter if you were in Seattle) - and transfer to your fabric of choice.
If it were mine, I think I would go with a two layer - a background of contrasting color, and then the logo on top of that - so it's really set off from the cover. There are lots of great fabrics that will go well with the cover...
Just for grins, I wonder what a sail person or canvas person would charge for it...
Also - keep in mind that I can send you whatever graphics you need, etc... Just let me know...
//sse