Fay...Just do wooden boxes...you can add liners and use treated wood.
If you want raised planters, I made these for $12 each! http://gatheredinthekitchen.com/2013/05/01/12-diy-planter-boxes/
I recently saw where someone spray painted popcorn tins and made the into planters.
Plastic or vinyl planters and pots are best around a pool. Metal planters can leave rust spots on the concrete surrounding most pools.