Thanks to all for the good advise. There just are not any inexpensive muscle boat or catamaran posters out there. Plenty of other sports covered though. (Freeze Frame had great stuff, just more than I wanted to spend.) Maybe I will contact the manufacturers directly and see what they can do. I will keep my eyes open for an inexpensive prop too. (Of course the ones I like on E-bay are pricey!) I personally liked the small cutouts idea. It got vetoed.
My son just told me not to worry about finding anything, so I will take my time and look around. Something will turn up eventually. Thanks again!