Yeah, sodium intake will cause fluid retention which can be painful, but I feel you on the heel pain. I went ahead and made the trip to a specialty shop where they make you stand on a platform that records your weight distribution and shelled out the cash for a good pair of insoles, and its helped immensely. They cost me about $50 but I only have to replace them every 14 months or so, as opposed to the cheapies which needed replacing every 3 and cost $11 a pair.
Even elevating my feet doesn't help. I'm not swelling much (yet), just when I eat a lot of salt it seems.