That does appear to be the next great hurdle, Jim.
In States where open carry is not regulated but CC is, those fees will probably be ruled as constitutional, regardless of the cost.
It is the states that ban the open carrying of functional firearms (thanks go to the CA legislature for making this easy), and CC is costly (and that includes not just the actual fee for the permit, but all costs associated with securing the permit) that will be the next big battleground. There are tons of case law on licenses and permits:
“A license is a mere permit to do something that without it would be unlawful.” Littleton v Burgess, 82 P 864, 866, 14 Wyo 173.
“A license is a right granted by some competent authority to do an act which, without such license, would be illegal.” Beard v City of Atlanta 86 SE 2nd 672, 676; 91 Ga. App. 584.
“A licensee is one privileged to enter or remain on land by virtue of the possessor’s consent, whether given by invitation or permission.” Wool v Larner, 26 A 2nd 89, 92, 112 Vt. 431.
“The licensor has the power to prohibit. Since the licensor is in the position to grant a right or permission it logically follows that he has the power to prohibit the act also. Likewise, having the power to prohibit something from being done, it follows as a corollary that power also exists to permit its use.” Taylor v Smith, 140 Va. 217, 235.
“The power to license necessarily includes the power to inhibit unlicensed persons from doing the acts authorized by license. The power to refuse license necessarily gives the power to limit the issuance of licenses.” Ex parte M.T. Dickey, 76 W. Va.576, 585; 85 SE 781.
“The power to tax the exercise of a privilege is the power to control or suppress its enjoyment... A state may not impose a charge for the enjoyment of a right granted by the federal constitution.” Murdock v. Pennsylvania (1943) 319 U.S. 262.
Without more, States licensing/permitting schemes are going to be restricted, where only one form of carry is allowed and that is regulated by the State.