In natural waters, calcium is considered an inhibitor due to its tendency to form a protective carbonate scale.  It also can form silicate or phosphate scales if these anions are present, either naturally or added as inhibitors.  Largely for these reasons (plus the presence of Mg), seawater is much less corrosive than an equivalent concentration of NaCl in DI water. – ASM Handbook vol. 13, Corrosion, p. 490+ and The Corrosion and Oxidation of Metals, p. 94-96.

The lower corrosivity of seawater vs. NaCl solution has been verified in salt spray testing per ASTM B117, although I don’t remember the reference. So, I would conclude that CaCl₂ is less harmful to your car than an equivalent amount (normality) of NaCl.  Came across this supporting statement:  “Calcium chloride has gained increased recognition as a superior deicing product, and highway mixtures with sodium chloride may be less corrosive than the use of salt alone.”
http://www.the-innovation-group.com/ChemProfiles/Calcium%20Chloride.htm

Unaware of CaCl₂ being less expensive than NaCl.  CaCl₂ production is more energy intensive, but perhaps the economics change if it is a by-product of ammonia production (starting from solid CaO or Ca(OH)₂ and NH₄Cl).

Not sure what rust inhibitors are used with de-icing salt, but strongly suspect that they are more effective with the CaCl₂ than with NaCl:
“Evaluations show that 25%, 30% and 32% aqueous solutions of the inhibited liquid calcium chloride produce just 4 to 7 mils/year of corrosion or 80% to 90% less corrosion than sodium chloride.  The tests compared sodium chloride, regular and corrosion-inhibited calcium chloride, and water.”
http://www.peterschemical.com/Calcium%20Chloride.htm

kenvlach
I was browsing and found your post.  Very informative. Thank you.