I have switched to Potassium Metabisulfite (called k-meta usually around here), which doesn't have the sodium problem, plus it's a powder and sold by the pound. Generally cheaper. And no sodium, although if you use the recommended amount of campden it shouldn't be a problem.
Both NA meta and K-meta are sold by the lb or bigger and even smaller but actually NA meta is cheaper and is a better sanitizer but even though the small amount we use in our wine is microscopic I prefer to use K-meta just because I feel I dont need any more sodium intake.
Also campden comes as sodium or potassium. I think that potassium is more popular. When I ran the store here in Canada, potassium (ie K-mets) was definitely more popular, as most suppliers didn't carry the sodium (Na-meta) version.