If you are sailing a Hobie 18 you are on the low-end cost and maintenance-wise for boat ownership. If you are not interested in racing and want just a lighter performance boat start looking at an older A-Cat in the 200lb range. You will get it cheaply, it will probably have aluminum mast, that is good cost-wise. It is heavier than the racing ones and that is why it will be cheaper. Still a fine ride and easy on the back compared to 400lbs.

Later,
Dan