As far as I know, a Cost Audit can definitely be performed by a CA. Qualifications for a Cost Auditor includes a Chartered Accountant. You can refer Sec.233B(1) of The Companies Act. It says that if in the opinoin of the Central Govt., sufficient no. of CWAs are not available, then a CA can perform such Audit u/s 233B. For details please read the relevant section.