I have owned numerous pairs of water shoes from the cheapies to the expensive ... there's not much difference unless you are a diver/snorkeler.  This time of year the discount stores sell cheapo water shoes that work just fine for strolling along the beach.  They're designed to get wet and protect your feet from rocks, coral, critters, etc.  Sandals or flip flops are too open and slip off - they don't protect your feet.  The expensive water shoes that divers/snorkelers use are somewhat different in that they fit better in fins, have heavier protection, etc.

If you need water shoes, go immediately to Walmart, Kmart, Target, etc. and buy the cheapest ones that fit.  I pack them in a plastic bag and wear good walking shoes and only wear them in the water.  I never wear water shoes all day... unless I'm on the beach all day which isn't a bad thing.