Go down to a RV (recreational vehicle/caravan) supply store and look at their stuff. Normally you will find things are considerably less expensive than "marine stuff." And sometimes the items are identical to the marine
version, just priced less.
Then look at your best/biggest home improvement (warehouse) stores. If possible find all plastic plumbing
units as they don't corrode in the marine environment
. But the standard brass/bronze units that are chromed work well for at least 5 years before the chrome gets too pitted and starts to fall off. But sometimes the prices are significantly lower and that makes their use cost-effective.