California Code, Penal Code - PEN § 28055

(a) For a sale, loan, or transfer conducted pursuant to this chapter, the purchaser or transferee or person being loaned the firearm may be required by the dealer to pay a fee not to exceed ten dollars ($10) per firearm.

(b) For temporary storage of a firearm pursuant to subdivision (f) of Section 28050, the seller, transferor, or person loaning a firearm may be required by the dealer to pay a fee not to exceed ten dollars ($10) per firearm.

(c) No other fee may be charged by the dealer for a sale, loan, or transfer of a firearm conducted pursuant to this chapter, except for the applicable fees that may be charged pursuant to Sections 23690 and 28300 and Article 3 (commencing with Section 28200) of Chapter 6 and forwarded to the Department of Justice, and the fees set forth in Section 31650.

(d) The dealer may not charge any additional fees.

(e) Nothing in these provisions shall prevent a dealer from charging a smaller fee.