To compare you need to know what strength the cal-hypo is. This is all fairly simple math, 1 gallon of 12% will raise FC 12 ppm in 10,000 gallons at a cost of $4.75. So you get about 40 cents/ppm/10,000 gallons. Assuming your cal-hypo is 48% (typically the lowest strength) then 1 lb will raise FC 5.7 ppm in 10,000 gallons at a cost of $1.70. So you get about 30 cents/ppm/10,000 gallons. If the cal-hypo is higher strength then the cost/ppm will be lower.
Since you are in California though I would think long and hard about using the cal-hypo. If you can do easy water changes then it won't be such a big deal, but if they can't easily change water then you are not helping your clients by adding more calcium. In this business reputation is everything, don't risk it to save a few dollars.