A quick estimate of my cost for Mineralyx barrels and $5 salt blocks for the past year divided by my total number of head including cows calves and yearlings is right about where you are - $30-32/head. I do buy a year's worth of Mineral-lyx barrels at my local feed store's annual spring sale which saves quite a bit on the regular daily one or two price. The feed store holds them and I pickup a couple of the paid-for barrels at a time thru the year as I return the empty barrels. The system works well.

Its really tough to come up with an accurate cost if you include calving problems avoided, health problems avoided, improved performance because of mineral...  basically my approach to mineral and salt is that "if it isn't broke don't fix it".  I had lots of problems with dry mineral when I tried it. I see no reason to go back.  Comparing ingredient lists, the Mineral-lyx tubs are hard to beat, and they are 100% consumed, essentially zero waste.