You might want to consider the new breathable waders. If you walk very far on the beach in normal waders you wind up being almost as wet, from condensation, as if you had fallen in.
I can only imagine what its like to walk long distances in neoprenes after having done a bit of scuba diving some time ago. Those wet suits are line sauna baths in warm weather.
After trying several types of waders, my conclusion is that they last a week or so longer than their guarantee. In most cases your only using your 1 year guaranteed waders for 6 months.
I'd follow Gene's advice and buy from a reputable company and get a guarantee which is proportional to the price. I'd figure on spending $50-$90 per year of guarantee.