Correct salt usage is dependent on quality of water coming into your site. I have one site that starts at 27 grains and another site that starts at 3 grains.
Number of bags used per month isn't a great comparison. That is like comparing your
soap cost on the cost per drum rather than the cost per car. If you want to compare with other washes, look at something like lbs of salt used per 10,000 gallons treated but make sure the wash has similar water quality coming in.
If you think you are overusing, turn back the regeneration frequency and test your water every day to see if the hardness starts to go up before a regen cycle. Finding someone that actually understands the process and can set it up correctly is valuable. I am pretty sure most car wash distributors know very little about water softeners.
We buy salt from Lowes. We called and talked to their commercial salesperson and got a better price than what is advertised. They deliver it and we buy 2-3 pallets at a time. Their price was the cheapest in our area.
David